Others have mentioned very good choices for messaging. For self-hosted audio and video calls, another option is OpenVidu Call: https://openvidu.io/openvidu-call
(that page also includes a demo deployment)
(that page also includes a demo deployment)
Appear.in went through some changes (not sure of exactly what) and became "whereby" (sincerely the previous name was so much better).
Another all time favorite of mine (not self-hosted though) is talky.io
And of course there is Jitsi Meet, a very well-known get-a-room application that can also be self-hosted. And they maintain a public deployment too.