I. Introduction: The Contract of Code

In the early stages of the internet's development, there was a "battle" that advocated for free cooperation in the computer age and opposed software proprietary that hindered technological progress, profoundly influencing the advancement of the public domain—it was the "Free Software Movement." This movement not only brought forth innovative open-source licenses but also sparked a wave of open-source software development, allowing the ideals of freedom and sharing to take root in the digital world.

Decades later, we stand once again at a crossroads of change. With the rise of Web3 and blockchain technology, the centralized economic paradigm dominated by humans is undergoing profound transformations. The development of personal sovereignty and the gradual questioning of platform capitalism dominated by large tech companies in the traditional Web2 era have led people to explore Web3, hoping to create an "ownership economy" where everyone can share ownership of the internet. Against this backdrop, the importance of "open-source" and "public goods" has re-emerged as key elements shaping the future economic paradigm.

Open-source software has become the cornerstone of today's technology and economy. Over 90% of global enterprises use open-source software, and open-source code has infiltrated 96% of commercial software[1]. This open collaboration model brings immense economic value—according to Harvard Business School research, the cost of building these codes from scratch without existing open-source resources would be approximately $8.8 trillion[2].

However, when we talk about "open-source" and "public goods," we often overlook a crucial foundational framework—open-source licenses.

The thriving development of open-source software relies on a reasonable licensing system, which not only determines how code is used but also profoundly influences the evolution of the software ecosystem. From Copyleft licenses to permissive licenses, different licensing models shape the boundaries of open-source software in commercialization, community collaboration, and intellectual property management. Today, code is becoming a contract, and technical rules are replacing traditional legal systems. In the Web3 era, "Code is Law" is no longer just an idea but a real-world evolution. In such a world, open-source licenses are not just norms for code usage but also core determinants of the structure of the internet economy and knowledge sharing. When code becomes a protocol and smart contracts replace legal contracts, the licensing of software directly shapes the boundaries of rights in the digital age.

Yet, amidst this discussion of freedom and sharing, there exists a more radical, controversial, and overlooked licensing model—the Public Domain Dedication.

Perhaps the Public Domain Dedication embodies the ultimate freedom. It allows developers to completely waive copyright, making software a true public good. Public domain licenses are still widely used in scientific research, cultural arts, and open data. However, their application in the software industry has been fraught with challenges: their legal status is controversial in some countries, they lack protection for contributor rights, and they are incompatible with modern software ecosystem incentives. With the development of Copyleft and permissive licenses, the role of public domain licenses in the modern technological world seems to have gradually been marginalized, like a tarnished pearl.

Fortunately, this pearl has a chance to shine again. The development of Web3 is redefining the contract of code, and the rise of smart contracts and decentralized protocols is giving new evolutionary directions to public domain licenses. With the advent of Web3 and blockchain technology, a new public domain licensing model is attempting to fill this gap—the SCC0 (Smart Creative Commons 0) license. Proposed by DAism, SCC0 aims to build a new governance model for Smart Commons, which not only inherits the spirit of public domain licenses but also combines the decentralized characteristics of blockchain technology, enabling Smart Commons and public goods to freely circulate in a truly public state without centralized licensing, while providing incentives to prevent contributor rights from being ignored.

If the Web3 era means that code will become the foundation of social governance, then how can SCC0 combine public domain licenses with smart contracts to ensure the sustainability of the sharing economy while safeguarding openness? When code is no longer just "code" but a contract for global collaboration, how will the future of the public domain be written? Next, let's delve into the past, present, and future of public domain licenses, exploring how this tarnished pearl can shine anew in the Web3 era.

II. The Past: The Origin of Public Domain Licenses

Public domain licenses are a member of the open-source license family. Therefore, to understand their evolution, we need to first examine the historical background and development trajectory of "open-source licenses."

In Web3, we have all heard of public goods and open-source applications to some extent. However, few people are aware of the "contract cornerstone" behind open-source applications—open-source licenses.

Open-source applications, also known as Open Source Software (OSS), typically refer to software where the source code is publicly disclosed to varying degrees by the licensor, allowing users to freely use, modify, and distribute the computer software under the conditions agreed upon in the license. Open-source licenses are the cornerstone of the open-source software ecosystem, clearly stipulating the license conditions for software usage, modification, distribution, etc.[3]. They ensure that developers retain copyright while granting users the "four freedoms"—to run, study, modify, and share the software freely.

These agreements are usually presented in written form, such as a text file named "LICENSE" or "LICENSE.txt" included in open-source projects. These files detail the legal terms and clearly specify how to use, modify, and distribute the code. For example, the GPL license requires any modified versions to be distributed under the same license[4], while the MIT license allows for more liberal usage[5].

In the early days of computing, software was often freely shared without formal licenses. However, by the 1980s, software gradually became commercialized. In 1983, IBM became the first large organization to release software on a large scale in a closed-source form. Proprietary software with closed source restricted users' rights to use, modify, and distribute through copyright and licensing, posing a threat to the free software community. In response to this situation, some developers hoped to protect the rights to freely use, modify, and distribute software. This need kicked off the Free Software Movement and gave birth to open-source licenses.

(A) Open-Source vs. Proprietary Software

Richard Stallman was a pioneer of the Free Software Movement. In 1983, he launched the GNU project, aimed at developing a free Unix-like operating system to counter the rise of proprietary software. In 1989, Stallman released the GNU General Public License (GPL), a standardized version of the copyleft license. The GPL ensures the four fundamental freedoms of software: to run, study, modify, and distribute. The release of the GPL is considered a milestone in the development of open-source licenses as it clarified the legal framework for software freedom.

It is through licenses that the open-source community establishes norms for contributors and users, making collaboration possible. Licenses specify which behaviors are allowed, legally protecting the spirit of open source. For example, the Linux kernel uses the GPL license, requiring any released modified versions to also be open-source, which forces companies using its code to open their source code, ultimately promoting community innovation[6]. Another example is Bitcoin, which initially chose permissive licenses like MIT, allowing anyone to freely use and commercialize it, attracting more developers to participate in the project[7]. Without the clear authorization of open-source licenses, the sharing and collaboration of open-source code would face legal risks, making it difficult to form a healthy ecosystem.

Open-source licenses directly constrain how others can use and disseminate code. For example, most open-source licenses allow commercial use, so anyone can use open-source software in commercial products. However, different licenses have different requirements for modification and redistribution: Copyleft licenses require derivative works to be open-sourced when released; while permissive licenses allow modified versions to be released as closed-source without forcing the sharing of source code[8]. This means that licenses like GPL encourage the sharing of improvements but may make commercial companies hesitant, while licenses like MIT are more friendly to businesses because companies can incorporate them into proprietary products without open-sourcing modifications[8]. For example, the GPL of Linux contributed to the open-source business model of companies like Red Hat, but it also prompted Android to adopt the Apache license in user space to avoid GPL obligations[6]. In short, the type of license determines the "contagiousness" of software in the distribution chain[8], thereby affecting developer adoption, community participation, and commercialization paths.

(B) Evolution and Branches

Current open-source licenses are mainly divided into three categories: Copyleft, Permissive, and Public Domain. Different categories have significant differences in licensing conditions:

1. Copyleft: Infectious Licenses

Copyleft licenses use the control granted by copyright law to require licensees to use the same license to open-source the source code when releasing modified or derivative works based on the original software. In short, it's the "share-alike" principle: you can freely use, modify, and distribute the software, but the works you contribute back to the community must also remain open.

Representative of this category are the GNU GPL series and the stricter AGPLv3 aimed at web services. Copyleft does not equal abandoning copyright or entering the public domain; instead, the author retains copyright and enforces the spread of freedom through license terms. The GPL requires that any product that distributes or distributes software containing GPL code must provide the corresponding source code to the recipient[9].

The AGPL further stipulates that even if the software only runs on the server side, if users interact with it through the network, the service provider must also provide its modified source code. Such terms aim to prevent someone from using open-source code to provide web services without feedback on modifications[10]. For example, MongoDB was once open-sourced under the AGPL but later switched to the stricter SSPL to protect its commercial interests, requiring companies providing SaaS services to open all related source code.

Copyleft licenses ensure that open-source software and its derivatives remain open, forming a "contagious" effect that benefits the public interest. However, this contagiousness is not friendly to commercial companies, which cannot use GPL code if they are unwilling to open their source code.

1. Permissive: Liberal Licenses

Permissive licenses grant licensees great freedom. Typical examples include MIT, BSD, and Apache 2.0, which allow anyone to use, modify, and redistribute software with few or no restrictions. The only requirement is usually to retain the copyright notice and license text. MIT released the X Window System in 1984 under the MIT license. The Apache license emerged later. The Apache Software Foundation released the Apache License 2.0 in 1999, a permissive license containing patent grant clauses that protect developers from patent lawsuits. This makes the Apache license particularly suitable for corporate environments.

Unlike Copyleft, permissive licenses do not mandate that derivative works be open-sourced. This means developers can mix code with proprietary source code or even release modified versions as closed-source software without violating the license[11]. Apache 2.0 also comes with patent licensing and indemnification clauses, further protecting users from patent lawsuits. The emergence of MIT and Apache licenses reflects the community's demand for more flexible licenses. The goal of permissive licenses is to minimize usage barriers and encourage widespread adoption and dissemination of software. Compared to the mandatory open-sourcing of GPL, these licenses allow developers to use code in closed-source projects, attracting more commercial companies to participate.

Due to their commercial friendliness (allowing closed-source secondary development and commercial distribution), many enterprises prefer open-source projects with permissive licenses. Among the three types of open-source licenses, the most widely used are the MIT or Apache licenses within permissive licenses. According to the "2023 China Open Source Annual Report"[12], the most used open-source license among active repositories on GitHub is the permissive license, accounting for up to 76.6%. For example, front-end frameworks like React and Vue use the MIT license; well-known industrial projects like TensorFlow and Kubernetes choose Apache 2.0.

Enterprises prefer permissive licenses because they allow software to be used in combination with closed-source code without open-sourcing derivative works, making it suitable for commercialization. The MIT license consists of only a short paragraph, making it easy to understand and implement. Although the GPL remains the core license for critical projects like Linux and GCC, its overall usage frequency has declined significantly. According to Black Duck Software data, the usage rate of GPL family licenses fell from 70.9% in 2008 to 24% in 2018[13].

1. Public Domain Licenses

The goal of public domain licenses is to legally waive copyright, placing works in the public domain and giving the public the greatest degree of freedom to use them. This concept emerged very early, but its development has been relatively slow. Donald Knuth released the first version of the TeX typesetting software in 1978[14]. In 1984, Knuth placed it in the public domain. This means that since 1984, TeX has been copyright-free, allowing anyone to freely use, modify, and distribute it. In those days, Knuth's approach was still rare, and the concepts of open source and free software had not yet officially taken shape, so public domain licenses did not form a systematic legal tool.

Strictly speaking, the true "public domain" refers to the complete expiration or waiver of copyright. In some countries or jurisdictions, copyright laws do not allow creators to directly waive their copyright or moral rights, leading to the emergence of legal tools

I. Introduction: The Contract of Code

In the early stages of the internet's development, there was a "battle" that advocated for free cooperation in the computer age and opposed software proprietary that hindered technological progress, profoundly influencing the advancement of the public domain—it was the "Free Software Movement." This movement not only brought forth innovative open-source licenses but also sparked a wave of open-source software development, allowing the ideals of freedom and sharing to take root in the digital world.

Decades later, we stand once again at a crossroads of change. With the rise of Web3 and blockchain technology, the centralized economic paradigm dominated by humans is undergoing profound transformations. The development of personal sovereignty and the gradual questioning of platform capitalism dominated by large tech companies in the traditional Web2 era have led people to explore Web3, hoping to create an "ownership economy" where everyone can share ownership of the internet. Against this backdrop, the importance of "open-source" and "public goods" has re-emerged as key elements shaping the future economic paradigm.

Open-source software has become the cornerstone of today's technology and economy. Over 90% of global enterprises use open-source software, and open-source code has infiltrated 96% of commercial software[1]. This open collaboration model brings immense economic value—according to Harvard Business School research, the cost of building these codes from scratch without existing open-source resources would be approximately $8.8 trillion[2].

However, when we talk about "open-source" and "public goods," we often overlook a crucial foundational framework—open-source licenses.

The thriving development of open-source software relies on a reasonable licensing system, which not only determines how code is used but also profoundly influences the evolution of the software ecosystem. From Copyleft licenses to permissive licenses, different licensing models shape the boundaries of open-source software in commercialization, community collaboration, and intellectual property management. Today, code is becoming a contract, and technical rules are replacing traditional legal systems. In the Web3 era, "Code is Law" is no longer just an idea but a real-world evolution. In such a world, open-source licenses are not just norms for code usage but also core determinants of the structure of the internet economy and knowledge sharing. When code becomes a protocol and smart contracts replace legal contracts, the licensing of software directly shapes the boundaries of rights in the digital age.

Yet, amidst this discussion of freedom and sharing, there exists a more radical, controversial, and overlooked licensing model—the Public Domain Dedication.

Perhaps the Public Domain Dedication embodies the ultimate freedom. It allows developers to completely waive copyright, making software a true public good. Public domain licenses are still widely used in scientific research, cultural arts, and open data. However, their application in the software industry has been fraught with challenges: their legal status is controversial in some countries, they lack protection for contributor rights, and they are incompatible with modern software ecosystem incentives. With the development of Copyleft and permissive licenses, the role of public domain licenses in the modern technological world seems to have gradually been marginalized, like a tarnished pearl.

Fortunately, this pearl has a chance to shine again. The development of Web3 is redefining the contract of code, and the rise of smart contracts and decentralized protocols is giving new evolutionary directions to public domain licenses. With the advent of Web3 and blockchain technology, a new public domain licensing model is attempting to fill this gap—the SCC0 (Smart Creative Commons 0) license. Proposed by DAism, SCC0 aims to build a new governance model for Smart Commons, which not only inherits the spirit of public domain licenses but also combines the decentralized characteristics of blockchain technology, enabling Smart Commons and public goods to freely circulate in a truly public state without centralized licensing, while providing incentives to prevent contributor rights from being ignored.

If the Web3 era means that code will become the foundation of social governance, then how can SCC0 combine public domain licenses with smart contracts to ensure the sustainability of the sharing economy while safeguarding openness? When code is no longer just "code" but a contract for global collaboration, how will the future of the public domain be written? Next, let's delve into the past, present, and future of public domain licenses, exploring how this tarnished pearl can shine anew in the Web3 era.

II. The Past: The Origin of Public Domain Licenses

Public domain licenses are a member of the open-source license family. Therefore, to understand their evolution, we need to first examine the historical background and development trajectory of "open-source licenses."

In Web3, we have all heard of public goods and open-source applications to some extent. However, few people are aware of the "contract cornerstone" behind open-source applications—open-source licenses.

Open-source applications, also known as Open Source Software (OSS), typically refer to software where the source code is publicly disclosed to varying degrees by the licensor, allowing users to freely use, modify, and distribute the computer software under the conditions agreed upon in the license. Open-source licenses are the cornerstone of the open-source software ecosystem, clearly stipulating the license conditions for software usage, modification, distribution, etc.[3]. They ensure that developers retain copyright while granting users the "four freedoms"—to run, study, modify, and share the software freely.

These agreements are usually presented in written form, such as a text file named "LICENSE" or "LICENSE.txt" included in open-source projects. These files detail the legal terms and clearly specify how to use, modify, and distribute the code. For example, the GPL license requires any modified versions to be distributed under the same license[4], while the MIT license allows for more liberal usage[5].

In the early days of computing, software was often freely shared without formal licenses. However, by the 1980s, software gradually became commercialized. In 1983, IBM became the first large organization to release software on a large scale in a closed-source form. Proprietary software with closed source restricted users' rights to use, modify, and distribute through copyright and licensing, posing a threat to the free software community. In response to this situation, some developers hoped to protect the rights to freely use, modify, and distribute software. This need kicked off the Free Software Movement and gave birth to open-source licenses.

(A) Open-Source vs. Proprietary Software

Richard Stallman was a pioneer of the Free Software Movement. In 1983, he launched the GNU project, aimed at developing a free Unix-like operating system to counter the rise of proprietary software. In 1989, Stallman released the GNU General Public License (GPL), a standardized version of the copyleft license. The GPL ensures the four fundamental freedoms of software: to run, study, modify, and distribute. The release of the GPL is considered a milestone in the development of open-source licenses as it clarified the legal framework for software freedom.

It is through licenses that the open-source community establishes norms for contributors and users, making collaboration possible. Licenses specify which behaviors are allowed, legally protecting the spirit of open source. For example, the Linux kernel uses the GPL license, requiring any released modified versions to also be open-source, which forces companies using its code to open their source code, ultimately promoting community innovation[6]. Another example is Bitcoin, which initially chose permissive licenses like MIT, allowing anyone to freely use and commercialize it, attracting more developers to participate in the project[7]. Without the clear authorization of open-source licenses, the sharing and collaboration of open-source code would face legal risks, making it difficult to form a healthy ecosystem.

Open-source licenses directly constrain how others can use and disseminate code. For example, most open-source licenses allow commercial use, so anyone can use open-source software in commercial products. However, different licenses have different requirements for modification and redistribution: Copyleft licenses require derivative works to be open-sourced when released; while permissive licenses allow modified versions to be released as closed-source without forcing the sharing of source code[8]. This means that licenses like GPL encourage the sharing of improvements but may make commercial companies hesitant, while licenses like MIT are more friendly to businesses because companies can incorporate them into proprietary products without open-sourcing modifications[8]. For example, the GPL of Linux contributed to the open-source business model of companies like Red Hat, but it also prompted Android to adopt the Apache license in user space to avoid GPL obligations[6]. In short, the type of license determines the "contagiousness" of software in the distribution chain[8], thereby affecting developer adoption, community participation, and commercialization paths.

(B) Evolution and Branches

Current open-source licenses are mainly divided into three categories: Copyleft, Permissive, and Public Domain. Different categories have significant differences in licensing conditions:

1. Copyleft: Infectious Licenses

Copyleft licenses use the control granted by copyright law to require licensees to use the same license to open-source the source code when releasing modified or derivative works based on the original software. In short, it's the "share-alike" principle: you can freely use, modify, and distribute the software, but the works you contribute back to the community must also remain open.

Representative of this category are the GNU GPL series and the stricter AGPLv3 aimed at web services. Copyleft does not equal abandoning copyright or entering the public domain; instead, the author retains copyright and enforces the spread of freedom through license terms. The GPL requires that any product that distributes or distributes software containing GPL code must provide the corresponding source code to the recipient[9].

The AGPL further stipulates that even if the software only runs on the server side, if users interact with it through the network, the service provider must also provide its modified source code. Such terms aim to prevent someone from using open-source code to provide web services without feedback on modifications[10]. For example, MongoDB was once open-sourced under the AGPL but later switched to the stricter SSPL to protect its commercial interests, requiring companies providing SaaS services to open all related source code.

Copyleft licenses ensure that open-source software and its derivatives remain open, forming a "contagious" effect that benefits the public interest. However, this contagiousness is not friendly to commercial companies, which cannot use GPL code if they are unwilling to open their source code.

1. Permissive: Liberal Licenses

Permissive licenses grant licensees great freedom. Typical examples include MIT, BSD, and Apache 2.0, which allow anyone to use, modify, and redistribute software with few or no restrictions. The only requirement is usually to retain the copyright notice and license text. MIT released the X Window System in 1984 under the MIT license. The Apache license emerged later. The Apache Software Foundation released the Apache License 2.0 in 1999, a permissive license containing patent grant clauses that protect developers from patent lawsuits. This makes the Apache license particularly suitable for corporate environments.

Unlike Copyleft, permissive licenses do not mandate that derivative works be open-sourced. This means developers can mix code with proprietary source code or even release modified versions as closed-source software without violating the license[11]. Apache 2.0 also comes with patent licensing and indemnification clauses, further protecting users from patent lawsuits. The emergence of MIT and Apache licenses reflects the community's demand for more flexible licenses. The goal of permissive licenses is to minimize usage barriers and encourage widespread adoption and dissemination of software. Compared to the mandatory open-sourcing of GPL, these licenses allow developers to use code in closed-source projects, attracting more commercial companies to participate.

Due to their commercial friendliness (allowing closed-source secondary development and commercial distribution), many enterprises prefer open-source projects with permissive licenses. Among the three types of open-source licenses, the most widely used are the MIT or Apache licenses within permissive licenses. According to the "2023 China Open Source Annual Report"[12], the most used open-source license among active repositories on GitHub is the permissive license, accounting for up to 76.6%. For example, front-end frameworks like React and Vue use the MIT license; well-known industrial projects like TensorFlow and Kubernetes choose Apache 2.0.

Enterprises prefer permissive licenses because they allow software to be used in combination with closed-source code without open-sourcing derivative works, making it suitable for commercialization. The MIT license consists of only a short paragraph, making it easy to understand and implement. Although the GPL remains the core license for critical projects like Linux and GCC, its overall usage frequency has declined significantly. According to Black Duck Software data, the usage rate of GPL family licenses fell from 70.9% in 2008 to 24% in 2018[13].

1. Public Domain Licenses

The goal of public domain licenses is to legally waive copyright, placing works in the public domain and giving the public the greatest degree of freedom to use them. This concept emerged very early, but its development has been relatively slow. Donald Knuth released the first version of the TeX typesetting software in 1978[14]. In 1984, Knuth placed it in the public domain. This means that since 1984, TeX has been copyright-free, allowing anyone to freely use, modify, and distribute it. In those days, Knuth's approach was still rare, and the concepts of open source and free software had not yet officially taken shape, so public domain licenses did not form a systematic legal tool.

Strictly speaking, the true "public domain" refers to the complete expiration or waiver of copyright. In some countries or jurisdictions, copyright laws do not allow creators to directly waive their copyright or moral rights, leading to the emergence of legal tools