2048x2048 is an implementation of that omnipresent puzzle game 2048, squashed down to 2048 bits -- that is, 256 bytes of executable code. Being an exercise in sizecoding it is written in assembly language, and the source is included with the game.
As with Gabriele Cirulli's original, this is a sliding-block puzzle played on a 4x4 grid, with tiles numbered in powers of 2. The cursor keys will shift all tiles simultaneously in one of the four directions, which also causes a new tile to pop up in one of the unoccupied squares. Tiles with different values will block each other's movement; if two identical tiles are bumped into each other, the pair will fuse into a new tile with double the value. The goal is to keep joining these identical pairs into higher numbers, up to 2048 and beyond, before the grid fills up completely (which ends the game).