A new Facebook-owned app is available today that gives iPhone and Android users the ability to create unique videos together. Riff is a side project created by a bunch of Facebook employees who thought that the world needed something where “if you could make videos collaboratively, the creative process would be more fun and the final product would be cooler.”
To create a Riff video you’ll need to start making a video, then share it with friends who will add to it, then those friends will add and share, and so on. Facebook notes that anyone will be able to see your videos, but only your friends can add to them.
[source] Google Play, iTunes [/source]