Alright, so here's what I came up with. It's USB-attached, but only for power. Next step, make it read the serial port and do what a Processing app tells it. Meanwhile, it's happy to loop randomly.
The loop() is very simple. It flips a coin to decide whether or not to glow red, then waits between 0 and 1000 milliseconds. It flips a coin to decide whether or not to glow yellow, and then waits between 0 and 2000 milliseconds. Finally it picks a random number between 1 and 8, and blinks the green lights that many times.