It was released earlier this week, and signifies Facebook’s continued efforts to compete with the likes of YouTube.
Riff takes the concept of video sharing and allows your friends to add to it. It starts with the user recording a 20-second video and uploading it to Riff (and to Facebook, by proxy).
Then, that user’s friends who are also Riff users will get a notification that a video has been uploaded. They’ll get the opportunity then to add their 20-second video to the Riff. These videos can be added on top of one another ad infinitum.
Sound confusing? Think of it this way: Facebook is trying to manufacture the next Ice Bucket Challenge.