Althought this isn’t mobile it is from binaura who makes some very nice Android apps.
Here’s the description:
Harmonizer is a musical instrument for studying diatonic scales through harmonic motions. Diatonic scales are serving as the basis for a wide range of music including folk songs, jazz, classical music. This instrument introduces modal scales, pentatonic and a few of the different minor / major structures. Harmonic motion is based on simple trigonometric pendulums (sinus, cosines, etc) that describes really organic motions. The goal of Harmonizer is to collide these two concepts and see what happens.
Try it yourself: http://www.binaura.net/stc/wrx/Harmon… (note: code is using Canvas & WebAudio. It has been tested with latest Chrome, Firefox, Safari (on OSX 10.7.5))