From the website:
8BITar Hero is basically Rock Band except with a Nintendo emulator generating the music and levels.
Gameplay levels that are procedurally generated from the act of playing a game. One person plays NES games on an emulator, others play a Rock-Band game with levels that are generated algorithmically from the audio code of the NES game. The focus here is the generative nature of the game, and the process by which the levels are created.