Matrix and Teamspeak are the big ones, ive seen people talking about XMPP and other self-hosted solutions. The real issue people are waking up to is that if you dont host your communication tools, you dont own them.

The self-hosting community is buzzing with people spooling up their own services and getting ready to abandon discord. If you or people in your circles need help setting stuff up, just ask. Plenty of helpful nerds and guides are around.