After some experiments with sound at pocketbook pro I have wrote small synthesizer programm for device. It base on ZynAddSubFX and can use its instruments bank.
It's not very quick (may be due to stylus event speen), but may be usefull. It can play single notes, quints, minor and major akkords (mode is changed by up,down,left and right buttons).
you can get current version from:
http://fedorchenko.net/nanosynth.php