This one's still ahead of its public launch, so there's no live user data to point to yet. What's built: a proximity-based sharing model for music discovery, aimed at the moment when the social music space intersects with people physically near each other.
It's an example of the earlier-stage end of the work here: taking a concept through to a working, testable product before it's in front of real users.
Deliberately vague ahead of launch: the mechanic is the product.