Parity, a game

Parity is a free, web-based puzzle game, in the same class as Threes and the like.

In Parity, you are presented with a three-by-three grid of numbers, with one of the numbers highlighted. You move the highlight into a new square using the arrow keys. When you move into a new square, the number in that square is increased by one.

The goal is to get all of the squares to have the same number. Simple to learn, fun to play.