Saltire is a connection game for two players: Black and White. It is played on the intersections (points) of an initially empty square grid (board). The top and bottom edges of the board are colored black; the left and right edges are colored white.
A crosscut is a 2×2 area containing two diagonally adjacent black stones and two diagonally adjacent white stones. A supercut is a crosscut along with eight additional stones orthogonally adjacent to like-colored stones in the crosscut.
Black plays first, then turns alternate. On your turn, place a stone of your color on an empty point or swap two orthogonally or diagonally adjacent stones. A swap must decrease either the number of crosscuts or the number of supercuts on the board, and it must not increase the number of crosscuts.
You win if there is a chain of orthogonally connected stones of your color touching the two opposite board edges of your color. Draws are not possible.
To make the game fair, White will have the option, on their first turn only, to swap sides with Black instead of making a regular move.
Saltire seems to be the first naturally finite orthogonal connection game with no captures, no placement restrictions and no chain reactions.
—description from the designer