Earlier quoted context omitted.
Newsgroups as in NNTP[1] fits those criteria, no? Granted, federated bit is more tricky now. Back in the days many if not most ISPs ran a NNTP server. But the protocol supports it. [1]: https://en.wikipedia.org/wiki/Network_News_Transfer_Protocol
I loved Usenet back in the day, but I sort of wonder why organisations keep their servers running. I struggle to find any active newsgroups these days. Weirdly enough spam still hits some of the groups.
I used Gmane[1] to access mailing lists as newsgroups, which I've always thought was a much better fit.
Alas as with all good things that was shut down also.