We've already got plug and dub for music, but if something's not on Youtube you're kind of ****ed. I'm still new to rabb.it but it's basically the same idea, but instead of playing the actual videos like plug or dub it actually loads whole webpages so that you are not restricted to Youtube. So far as I can tell the sky's pretty much the limit with rabb.it so long as you can find something on the internet.
Plug's still fine for music, but we could easily use rabb.it for movies (no more worrying about being able to find something on Youtube for Movie Night), tv episodes, streaming sports events, and probably a million other things. Apparently you can even do voice and video chat as well as the usual chatroom style ****.
rabb.it