@mray This is a nice depiction of the current state :)

Strictly speaking, it is several social networks communicating in a federated way, ActivityPub being the protocol that unified communications between several projects, but the Fediverse existed before it, protocols were heterogenous and bridges existed between some parts of these federated universes. Some of them are still there and apart of ActivityPub. To me, they form the Fediverse too. More like a multiverse linked by special gates :)