The number one thing for me as a developer is how things on Ethereum are composable and built on open standards.

For example, USD Coin and Wrapped Bitcoin are smart contracts (a program running on the Ethereum network). They store user balances in their own internal state and expose a standard API called ERC-20 for modifying it. Other smart contracts can talk with USDC, WBTC, and every other token using the same ERC-20 API.

DeFi (Decentralized Finance) has been called 'money legos' because of this composable nature. An example of a basic DeFi protocol (here in DeFi, protocol means something like a stateful system rather than a way of communicating) is Uniswap, which is an exchange. It holds balances of tokens and lets people swap between them according to its pricing formula.

When someone wants to buy WBTC, they first approve an allowance to Uniswap, then Uniswap pulls the funds and returns the corresponding amount of WBTC according to the pricing formula. It works for every token, because all tokens implement the same common APIs which Uniswap uses too.

Another example of a basic DeFi protocol is Aave. It's a lending platform that lets people take out loans against their crypto collateral. This means they don't need to sell if they need to pay bills, for example. They can simply borrow against it.

A more complex example is Yearn, which is a yield optimizer which takes your money and rotates it between different strategies to get you the best rates on your savings. It talks with Aave, and Morpho, and Euler, and all those different DeFi protocols using their APIs.

Not only is it composable, Ethereum DeFi is permissionless. This means that no one can stop you from building your own smart contract to interface with others for your own purposes.

And not only can you build finance, but you can also build governance onchain. DAOs are smart contracts that can manage money by vote of your organization. Arbitration protocols like Kleros allow people to make escrow deals. Etc.

Pretty much, Ethereum is the New Internet: a world of relationships between autonomous, open source code. Traditional finance is sort of like this, except instead of code, paperwork is used to compose businesses together. + Ethereum is much newer than traditional finance, so lacks a lot of the tech debt it has (clearinghouses, settlement, all those hacky solutions, ancient regulations)

This is not only limited to primarily financial assets. As the world goes onchain, more and more things will be 'tokenized', i.e. making it usable through these APIs.

An instance right now of a somewhat non-financial asset is ENS Domains. The fact they are tokenized means they can be held by DAOs or multisigs (smart contracts that require multiple different signatures to confirm a transaction) natively, allowing groups of people to manage these assets collectively.

Decentralization wins because decentralization lets more people build together. The more we build, the stronger we become. No need to for permission, just open APIs that anyone can write smart contracts to use.

Now wouldn't that be something great?