peertube,

diaspora,

and kinda forgefed/forgejo, but it’s not really going many places yet.

oh! and a smattering of others i’d forgotten about… like microblogging things… gnu social? pleroma? and others i forgot even harder. [edit, oh, and friendica ~ meh]

i’ve heard irc be described as federated too. ~

[edit, and now piefed too, thnx to another comment here]