Web RTC – http://www.webrtc.org/
http://www.html5rocks.com/en/tutorials/webrtc/basics/
https://appear.in/ – WebRTC form of Skype. Better quality, better performance. Chrome, Firefox, and Opera only.
https://pingo.upb.de/ – Pingo (free to students & teachers)
http://www.simplemeet.me/ – Online chat with simple code that you enter to join a room
http://todaysmeet.com/ – Backchannel service that creates rooms and integrates Twitter hashtags