51% Attack. When more than half of a blockchain’s computing power is controlled by a single agent, it can carry out malicious transactions against the network. For example, spending the same coin more than once. Altcoin. Any cryptocurrency other than Bitcoin. The most important altcoins are Ether, Ripple, Litecoin, Monero, Zcash and Dai. Bitcoin. The first cryptocurrency based on blockchain technology. The paper was published under the pseudonym Satoshi Nakamoto on October 31, 2008. The netwo...