UPDATE: Prisoners' Dilemma won first place in the innovation category for LD34!
Prisoners' Dilemma is a two-player game played across the Internet. It was made for Ludum Dare in December 2015 and implements the "two-button controls" theme. If two players are present, then they are placed in a prison together. The only way that they can communicate with each other is by knocking on the wall that separates their cells (using the K key on the keyboard). They can also attempt to escape (with the D key), but will be killed in the attempt unless they synchronize their attacks and each take down a guard. The difficulty of the game, then, comes from the fact that it's quite hard to synchronize an attack when you have no means of communication other than knocking on a wall.
Prisoners' Dilemma was made with p5js and nodejs.