Unfortunately, Microsoft is still doing its own thing with CU-RTC-Web. Everyone else supports the WebRTC draft.
http://www.tokbox.com/blog/what-the-cu-rtc-web-vs-webrtc-debate-means-for-developers/
Firefox Hello does not support group chat either :( . I've read they are based on OpenTok and this protocol supports group chat, but it's not yet available in Hello. Will be eventually, though.
http://www.tokbox.com/blog/firefox-hello-mozilla-enhances-opentok-powered-video-chat-service/
There's probably lots of ways to do such websites but using nodejs and some of its packages will help you make one.. I found a tutorial on how to make a "chatroulette" here: http://www.tokbox.com/blog/creating-chat-roulette-with-node-js-socket-io-and-opentok/
Attended a conference lately and one of the sponsors was promoting their new product, Tokbox.
Pretty slick, actually. Very easy to use API and it's completely free. Worth looking into, at least.