fizzle

I’ve been trying to get zulip working.

Sounds like it addresses your requirements.

Seems to be a real bitch to self host - I’ve been doing this a while but the compose yaml is pretty arcane with hundreds of environment variables.

I didn’t “give up” exactly but it’s been on the back burner for a month or so now.

I’m honestly kinda surprised that Google is apparently not in fact doing this already and (according to the comments here) continues to not do so.