There’s also Matrix, but it kinda sucks. (We have both it and XMPP.) It handles encryption key management infinitely better than XMPP though.

(Haven’t used Deltachat.)

(If you’re selfhosting or trust your server, and the people you’re talking with are selfhosting or trust their server and you trust their server, you probably don’t need end to end encryption and XMPP without E2EE will work fine.)

– Frost