There's also pleroma, which I've run and is pretty great and low on resource requirements. And there are tons of other social UX paradigms like link aggregators and even Peertube which is a tube site server on the same network as mastodon using the same ActivityPub protocol.
I'd love to see people implement novel types of social sites besides functional clones of existing social media, there are some significant architectural and UX differences in a distributed, federated social architecture that can be leveraged to great effect.