If i had to make a comparison this would be sort of playing a game in Co-op mode except...for programming. From an article I read this application was developed in the Mozilla labs. Its still in early development though (current version is 0.2.2).
One of the most interesting features (according to the article) is the ability to code online with someone else simultaneously. The application was built to be very fast even with big projects. And of course with it being online it's accessible from anywhere that has an internet access and it also happens to be free.
Now I haven't had the chance to try it yet. I'll probably just create an account and ask one of my friends to login as well just to see how well this co-op mode the article talks about really is like. I'll report back here when I do
-Borg