@cosine Don't know of anything. Never found voting side of the axis all that interesting.
That said, I could easily imagine a federated alternative built atop the same sort of architecture as Mastodon. You've got posts, replies, upvotes and a primitive namespace (hashtags). Just incorporate downvotes, and maybe optional namespace moderation, and the rest is just how the UX presents threading within each namespace.
@cosine Sounds like a programming challenge worth pursing.
The advantage of federation is that you get past the silo trap. Sure, an instance might be all socialism. Another instance might be all tech, but the "hive mind" wouldn't be limited to any given instance.