andrew@ThisIsLeeloo I definitely wasn't around for it, but I know friendica, diaspora and GNU social's predecessor were around separately since 2010. They only connected with each other years later, though, through changes in protocol. So I'm not sure how concrete of a start date there is to the fediverse.
The current ones Mastodon is interoperable with are GNU social, Friendica, Pleroma, and PostActiv, I think?
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