I've open sourced my project SoundTab:
Play like on Theremin, but instead of moving hand in the air,
move pen over wacom tablet. Volume is modulated by pen pressure,
instead of left hand movement in Theremin.
For better experience, use Wacom digitizer with pressure
You can play with mouse as well, but w/o volume modulation (no
pressure information), and less precise positioning.
Supports only Windows so far.
Binaries may be downloaded here: