I'm doing Negotiation, Conflict Management, and Therapy simulations. Our prototypes were in JIbe. We're now using a Hybrid of Jibe and our own code.
We replaced Vivox with WebRTC via OpenTok. There are two modes one that is a drop in replacement for Vivox and the other is webRTC on it's own. With WebRTC on its own you can add video as well as voice.
We ran 3 simultaneous sessions with 20 people in each session. That's about the max without provisioning more resources.
If you've got any questions let me know.
--Rick