XMPP (aka Jabber) is the community-owned standard for real-time federated messaging.
JoinJabber.org admin support chat
For messaging is recently tried SimpleX with a group of people I know.
It's very nice, it's open source, does not require a phone number, is e2e encrypted, has a very nice UX and UI and is decentralized.
By curiosity I try to setup my own server and it was up and running in 20 min. I was really impressed by how easy it was.
I have not try it for very long yet but so far I find it better than Signal.
What I’ve seen of the protocol, their business model, and what they say about their implementation, very tied to the Amazon infrastructure (an infrastructure managed by an American company, so much for sovereignty)
Does anyone know how Open Stack has been working out? It was supposed to challenge the supremacy of Amazon Web Services, but that doesn't seem to have happened. Only a couple of large institutional users have successfully deployed Open Stack solutions, and since each deployment requires so much specialist knowledge and site-specific configuration, it seems very difficult for non-affiliated people and institutions to use the system. And it doesn't seem like Cern, NASA, or other participants are doing a very good job of distributing knowledge of how their systems work outside of their closed institutions.
I didn't know this even existed, thanks for the link! That list of challenges doesn't seem that unsurmountable though