Make theme variations in more creative way

Riff, Facebook’s newest app, invites users to create variations on a theme with their friwvends in a visual way. So if you wanted to start a riff showing off your best silly face, you’d shoot a short clip of yourself getting goofy and then send it around to your friends. Ideally the finished product would be a compilation of short videos of friends hamming it up, except maybe your one super-serious and disdainful friend. (We all have one. If you don’t, it’s you.)
It’s a fun idea, though one that’s most fun when your friends jump in. The app is integrated well with Facebook, but is hardly highlighted by the main social network as a key feature.
All in all, this feels like what it probably is: a fun side project from Facebook with the potential to take off if it finds its audience. Free, for iOS and Android.