Single-player tile-matching game, commonly known as Mahjong solitaire.
Tiles are stacked on the board at the start of the game. The goal is to
remove all the tiles in as little time as possible.
Select two matching tiles and they will disappear from the board, but
you can only select a tile if there is an empty space to its left or
right at the same level. Be careful: tiles that look alike may actually
be slightly different.

You can choose from a variety of starting layouts, some easy and some
difficult. If you get stuck, you can ask for a hint, but this adds a
large time penalty.