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
openvidu is nice, in many ways it looks very similar to google meet. And the "get a room" functionality reminds me of a system I used to use long time ago called appear.in (seems they are out of business..)
I work on the OpenVidu development platform thus the Call application example was an easy recommendation... we have a public server with demo deployments, of which Call is just one.
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.