h.fbk is an instrument made to produce the sounds of harmonic feedback. Do you like the sound of guitar feedback, not the squeally stuff, the rich, evolving, shimmering notes. Well I do too! This instrument contains 15 touch sensitive points relating to 15 harmonic frequencies, put together with some custom distortion and resonant feedback.
Try placing two fingers anywhere on the screen, then move them into different positions. Experiment with different touches, few or many, slow movement or fast.