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Wave your hands over it, press buttons, turn knobs. It makes wacky sounds!
It's a two channel buzzer that changes it's waveform output based on moving your hands over two photoresistors. Potentiometers and buttons also change the frequencies and pulses, respectively.
VIDEO of circuit here.
This circuit relies on the CD4093 (quad NAND Schmitt Trigger) and a few passives to oscillate output to a small piezo speaker. The design is inspired by those seen in Nicolas Collins' book Handmade Electronic Music