If you would prefer to self host, there's always FreeSWITCH [0]. It can act as a server for meetings. There is a webRTC client called Verto Communicator that seems to work quite well, or you can use SIP clients.
The documentation is a bit lacking, but it's actually a very capable system for unifying voice, video and chat communications – and a whole lot more.
I run a IRC server @ irc.letschatlinux.com. We are a small but growing community that loves Linux and open source solutions. We are also friendly and drama free! Check us out in #welcome.