An older project, but one worth adding an entry for - I still hope to revive this eventually. Me and two other guys built a very much working version of it over the course of a night, and won some swag for it too. When the semester ended, I spent roughtly 3 weeks working very intensely on it, to the point that I got it published in the Play store. It could do so much! Not only did it produce awesome graphs based on your music collection, but it was a full featured (well, sort of) music player, for some reason.
After much work I released it, to no fanfair, and eventually forgot about it. One day, I returned to check in on it, and found that the API we used to access Google Music was dead! And so, too, was MetaMusic. But! One day, this shall live again.