Dropchord is $2.99 for iOS devices and can be downloaded through the App Store. [Direct Link]Dropchord is a music-driven, score challenge game with mesmerizing visuals and an original electronic soundtrack! Influenced by music visualizers and score attack arcade games, Dropchord is an original experience that'll test your dexterity while providing endless fun!
Dropchord is also available for Leap Motion on OS X.
Article Link: Double Fine Productions Launches 'Dropchord', a Rhythm Game for iOS