Although Nakamoto's system is not perfect, his/hers/their proposal was the face that launched a thousand ships and inspired many others to form their own open networks. For example, the second most well known system is Ethereum, also released via whitepaper by Vitalik Buterin when he was just 19 years old! Like Bitcoin, Ethereum has a cryptocurrency, but what distinguishes it is that it allows users to create applications on top of the Ethereum blockchain technology ("decentralized applications", or dApps") via smart contracts (IF this THEN that). It's a decentralized application to build decentralized applications. So for others to build their dApps, they can use Ethereum instead of trying to start from scratch. To feature some other cryptocurrencies, there's also many hard forks (a hard fork is when a cryptocurrency splits into two due to disagreements between users) from Bitcoin such as Litecoin, Bitcoin Cash, Bitcoin SV, and others such as Decred, Monero, Zcash, Tezos, etc.