Facebook has a whole division called NPE that often comes up with new apps and services, and many of which get buried frequently too. The latest experimental product to come out of NPE is an app called BARS that is aimed at aspiring rappers.
It allows users to pick one from a library of professionally-created beats and rap along to make a dope video. The core premise here is that not everyone has access to studio-grade tools and instruments to make beats for their rap verses, which is where BARS is trying to bridge the resource gap.
There'll be audio effects like auto-tune, in case you happen to be a T-Pain fan.