You might want to have a look at WebRTC. I haven't tried it, but here's the first multiuser demo that I'm aware of: https://github.com/webRTC/webRTC.io
Some discussion about it (and how I know of the project) can be found in the webrtc-discuss Google Group at https://groups.google.com/d/topic/discuss-webrtc/26UNDNm-q0w/discussion
For more information about WebRTC in general, see also:
- http://www.webrtc.org/
- http://en.wikipedia.org/wiki/WebRTC
- http://www.html5rocks.com/en/tutorials/webrtc/basics/
Good luck with your project!