Kaltura
Kaltura is a free online site for group video making. This is one of the first tools that I know of for creating rich media collaboratively.
"Users who start a Kaltura choose its topic, pick a look for the Kaltura page, and invite friends to contribute video, music and photos to it. Then, they can even edit it together. The collaborative result can be viewed on Kaltura.com, downloaded for later use, and easily embedded on any site, blog or social network as a widget."
Take a look at the video that explains more:
