A very simple plugin for the Ethereal Dialpad application from Adam Smith (https://market.android.com/details?id=as.adamsmith.etherealdialpad), which uses multitouch.
With one finger on the screen, a circle appears and music plays.
With 2 fingers, circle radius changes and played note changes as well. More precisely, the note played is located between the 2 fingers, allowing you to produce quick alterations.
Note: You must also install Ethereal Dialpad to use this app. To run it, run Ethereal Dialpad and select Circle Melody Pad in the plugins list.