Is it any service that includes the ability to federate? If so, are Matrix/XMPP/other non-ActivityPub services part of the Fediverse, or does Fediverse really just mean ActivityPub?
The context is wanting to promote a Matrix chat room on discuss.online: #online.discuss:discuss.online (see post). Does it belong in Lemmy communities like this one, !fedigrow@lemm.ee, etc? Or does it not count as part of the Fediverse?
I think by now pretty much everyone here heard about Matrix at some point or another.
Personally I think Matrix and XMPP belong go the Fediverse in the loose sense. ActivityPub isn’t designed for messaging, and they offer good protocols for that.