Really hoping that proliferation of instances will lead, in time, to divergence in modeling (at the software level) the parameters of "community" and sociality.
GNU Social/Mastodon shares features with SMTP, IRC, Usenet (surprised not to have seen that mentioned by others), with BBS networks before that, and even such antiquated systems as postal newspaper exchanges. In this history, "social media" giants are distinct only in their resort to centralization.
The organizing model is unchanged.
Generalistic and moderated instance.