Crosfor (from Welsh: croesffordd, meaning «crossroad») is a drawless connection game for two players: Black and White. It is played on the intersections (points) of a square board initially empty. The recommended size is 19 points per side, although boards of 13, 15, and 17 are also valid. The top and bottom edges of the board are colored black; the left and right edges are colored white. Each player has a sufficient supply of stones of their color.
Definitions:
An empty diagonal is two friendly stones adjacent diagonally, without friendly stones orthogonally adjacent to both; otherwise, it is a full diagonal.
To reinforce is to turn an empty diagonal into a full one.
To flip is to replace an enemy stone with a friendly stone.
Turns:Black plays first and then turns alternate. On your turn, perform these actions in the indicated order:
Place a stone of your color on an empty point.
Reinforce all friendly diagonals that arise after your placement, doing so through placements or flips.
End of the game:You win by connecting your two sides of the board with a continuous path of your stones.
To balance the game, before starting, the first player places a black stone on an empty point and the second player chooses a side. This balancing method is called the pie rule.
—description from the designer