From CCRMA Wiki
This instrument uses the slorkian fret-based mapping to trigger notes. It has been modified to allow polyphony.
How to Play
Pressing alphabetical keys triggers notes. Releasing them releases notes.
Moving the trackpad along the x-axis performs a filter sweep with a moderately high resonance.
Moving the trackpad along the y-axis detunes the sound's multiple oscillators from one another.
Pressing any of the digit keys 0-9 selects a different ADSR envelope setting for all notes triggered after the digit is pressed. The envelope settings are arranged logically such that towards digit 1, sounds are more percussive, and towards digits 9 and 0, sounds are pads.
Here is the chuck file. Note that you may use a mouse rather than the trackpad to give the instrument a different feel.