I’ve looked for alternatives lately and the most promising one I’ve seen is Spacebar. I would like to see it federate eventually, but I think the way to attract users fleeing Discord isn’t to make them adjust to a less-intuitive or less-featured alternative. People switched to Discord because it combined feature-rich text chat with group voice, video, and streaming all in one central place. Going back to Mumble, Teamspeak, etc. for voice, Matrix or XMPP for chat, etc. is a downgrade and people will just put up with Discord if that’s the alternative.

Unfortunately, there are no fully feature-complete alternatives with Discord’s user-friendliness yet. Spacebar is at least going in the right direction, trying to completely replicate Discord’s API. It seems they had voice working at one point but it’s currently broken due to a compile issue, hopefully the influx of new users will expedite a fix. The only major other thing they’re lacking then is streaming, though that doesn’t sound too hard if they already have voice working. The devs have said they’re open to federation as a future upgrade but the current focus is fully implementing the Discord API. A self-hostable Discord is pretty much what I’d want as a replacement. I’ve used Mumble and I’ve used Matrix and I agree with the idea that neither are a proper replacement for Discord. Matrix’s communities are a loose collection of independent rooms, which is not the same as a proper Discord guild/server. Matrix is great if you want secure, encrypted chats, but synchronizing keys is a pain I don’t see most Discord users accepting.