You could also try Movim. You could have a decentralized XMPP server with a client that support group calls as well as having posts like a forum folks can comment on.
There are a bunch of options out there (though I've never seen Movim - thanks, I'll check it out) but most communities seem either to be on Discord or Matrix (with a few still hanging on to IRC and a few others on Slack) - Discord being by far the best UX of the lot.
