I’ve released my 1st iPhone app “ArtooSynth”.
ArtooSynth is a synthesizer can be played with one finger.
Sound like “R2-D2’s Voice” though.
To the point that you have touch, you can display the colored circle.
enjoy! 🙂
ArtooSynth : http://www.takahirokoyanagi.com/app_ios/artoosynth.html