Controls are w and up arrow, for the the first and second players, respectively. As you hold down the key, steam pushes the paddle upward, otherwise gravity takes over.

I accidentally forgot to take the ball speed off of 0 before I posted SteamPong. If you want to play the game with a moving ball, go to line 182 of the source and change the speed variable from 0 to 7 (which is what I recommend, so that there is a standard speed across the judging of my game). Thank you for taking the time to correct my stupid mistake.