The game based on beats. No seriously, the whole game revolves around a user selected masterpiece.
Essentially, this game is a rhythm game with audio analytics built in which allows the user to choose the tracks of which they play to.
This game uses LibGDX which is a very impressive game framework/engine. Its completely written in Java, and supports multi-platform pretty well. Go check them out.
This game also uses the Jtransforms library for its fft functions. You can go and read up on what they do.