I discovered this recently, and it's pretty damn cool.
So apparently Synchtube is this web application that allows you and the people in the room to simultaneously stream the exact same media. Use it to watch movies, for example! Great stuff. I got introduced to it by getting linked to The Odd Music Box.
How does it work? You join in, and listen to the songs that are being added to the playlist by the people in the room. If we're running low on songs, we call a command that adds five random songs to the list from a database of songs that have been added before. And if you want to add your own, just register (takes less than a minute), and you'll be ready to go!
The folks over there are really nice. I've been talking to them regularly for the past few days, and it's a great place to hang out.
Not to mention all the new music you get to hear. Such a wide variety of genres, too. (Though rock, metal and electronic do prevail a little bit.) Lets you discover new artists in a pretty cool way.
So yeah, check the room out, and maybe I'll see you on there sometime!