Digitz! is a free online multiplayer game providing you hours of mind-bending fun. Even being absolutely mathematically challenged, I discovered a simple fun of addition with help of Digitz! The point is to swap letters over the free cells on the playfield so that adjacent letters would make up a required sum. Say, if you are required to get 10, you are to place 3 and 7, 2 and 8, 1 and 9 etc. on the adjacent cells of the playfield.