I made Pong!
Controls are: up and down arrows for right player, w and s for left player. Click to reset when the game is over.
I stole most of the calculations from this rubyconf video, because I don't remember enough math.
This was the first project where I've had to deal with a memory leak before; I'm pretty sure it's solved now, but it was frustrating to track down (protip: all your objects should be able to deconstruct themselves and their event listeners).
But still - Pong!