Hypercore
Distributed append-only log.
Hypercore comes with a secure transport protocol, making it easy to build fast and scalable peer-to-peer applications. Think lightweight blockchain crossed with BitTorrent.
Hypercore currently serves as the foundation for a diverse range of P2P applications, including chat apps, filesystems, databases, and even a browser for the distributed internet. And the whole thing's MIT-licensed, so you can use it as you like!