Firefox Hello – video calls/video chat
This video calling feature from Firefox uses WebRTC compatible browsers (Firefox & Chrome are 2 that support it right now). No account setup is required, send a link to the chat and they can join the call with you.
No connection that I see (yet) for a broadcast like a Hangout on Air, and I've not really learned all the details, but the fact you can do a video call with someone without needing to sign in or register will be helpful to many until they run into more limitations.
I've attached this short intro video on FireFox Hello: https://www.youtube.com/watch?v=TEPq4xFGzG0
Here's the official announcement page from Firefox/Mozilla:
Both users in Firefox works, or one starting in Firefox and the other joining via a link in Chrome could work as well (both support WebRTC).
I'm sure that we'll see more about this soon. It apparently is not a new service, but it has just been re-released.
Update: I've done a review on how this works including annotated screenshots here: http://goo.gl/LRRctr