@chara there are several protocols for federation though don't know how well they compete with ActivityPub (giving most software that supports those other protocols also support ActivityPub they probably mainly act as fall back protocol if they can't use AP for some reason), and AP is a W3C standard so probably not.
@chara Actually mastodon supports Ostatus as well AP, but AP was derived somewhat from Ostatus with the xml/atom repaced with json. There is a wikipedia page that lists all federative social network software and the federation protocols they support.
@Codeawayhaley @email@example.com Yeah, I think that's the only bit left. After a point, it stopped actually communicating with OStatus instances, which had the Gnu Social nerds' knickers in a twist.