Jitsi Meet is a WebRTC-powered multi-user videochat.
For a live demo, check out https://meet.jit.si/.
Please also check out the beta: https://beta.meet.jit.si/.
More info at https://jitsi.org/Projects/JitsiMeet.
Jitsi Meet started in 2013, emerging from Jitsi Desktop which had started in 2003.
See also Jitsi Desktop.