Another demo which has been sent to gbadev, this time by OrR:

our friends all play piano, trumpet or violin? Now you’ve finally got your own instrument! With this useless little program your GBA can beep 3 octaves! You only have to press the right button combinations.This program really doesn’t make much sense… But it’s my first GBA program! Indeed my first program for a really long time… This explains why it’s so simple, stupid and in spite of that the code (done with DragonBasic, should be included in this zip along with the really lovely background that might as well be a screenshot…) is a lot of crap…

http://www.gbadev.org/