If you've got time to kill (anywhere from 20 seconds to a few hours), iShisen might be right for you. Shisen-Sho (“Four Rivers”) is a tile matching game. The objective is to remove all the tiles from the board in the least amount of time. Matching tiles can be removed if they can be connected with three or fewer horizontal and vertical lines. Lines may extend around the outside of the board, but may not cross over other tiles.