Jitsi

No chat only? .... community.jitsi.org/t/chat-function-only/79067

As of 2020: end-to-end encryption optional and turned off as default, and marked as experimental...

Appears to be based on XMPP: community.jitsi.org/t/jitsi-users-is-jitsi-a-regular-xmpp-server/13211