2048 is a single-player sliding block puzzle game by Italian web developer Gabriele Cirulli.
The games objective is to slide numbered tiles on a grid and combine them to create a tile with the number 2048. Use the arrow keys to move the tiles in any direction. If two tiles of the same number collide while moving they will merge into a tile with the total value of the two tiles that collided. The game is won when a tile with a value of 2048 appears on the board.
The Wikipedia article on 2048 can be viewed here