Fun with RAM
AtariAger Thomas Jentzsch first brought up the idea of making games using only the Atari 2600's RAM, which means the game would have to be 128 bytes or less. Here, I'll list the various games that do just this as well as their authors and notes.
Combat by "Wickeycolumbus".
Pong by Thomas Jentzsch, uses paddles.
Tic-Tac-Toe by "Zach" uses keypad.