Facebook's Creative Labs has spawned plenty of hits and quite a few misses in recent times, ranging from Paper to Facebook Groups, and today, has thrown out another interesting concept in the form of Riff. It's a concoction of services like Slingshot and Snapchat, allowing users to create and share videos of up to 20 seconds, with the general idea being that other users will add their own bit of footage running along a similar theme. So where you'll have single, short videos, users will also be able to create Stories a la Snapchat, but in a combined effort as everyone chimes in with their clips.