This is an interesting music app / game from Zach Gage maker of the excellent SynthPond and Sonic Wire Sculptor.
“A Generative Musical Instrument – Halcyon features a complete generative soundtrack that becomes an instrument when you play the game. Since its designed to accompany you while you play, you’ll create tranquil sonic landscapes as you travel along. Gameplay is one part spacial action puzzler and one part interactive stringed instrument combined in an experience designed specifically for the iPad. Colored currents travel inexorably toward each other. Strum the strings to match the currents, creating both phonic and visual harmony.” – zach gage
Interested? Take a look at Halcyon priced at $3.99.