This is a bytebeat synthesizer implemented on the Arduino. It's not the first bytebeat synthesizer on the Arduino, but I think it's the first that does real-time composite video visualizations of the signal, using the TVout library hacked to remove its audio output.
It doesn't have any user interface yet; you have to edit the code to change which formula it's producing.
I'm running it on an Arduino Duemilanove. Pin 11 has the audio signal, pin 9 has sync (through a 1-kilohm resistor), and pin 7 has video (through a 470-ohm resistor).