Gomoku, also called Five in a Row, is an abstract strategy board game. It is traditionally played with Go pieces (black and white stones) on a Go board, using 15×15 of the 19×19 grid intersections. The game is known in several countries under different names.
Players alternate turns placing a stone of their color on an empty intersection. The winner is the first player to form an unbroken chain of five stones horizontally, vertically, or diagonally.
Besides many variations around the world, the Swap2 rule (based on “swap” from Renju) is currently adapted in tournaments among professional players, including Gomoku World Championships.
In Swap2 rule, the first player starts by placing three stones (2 black and 1 white, if black goes first) on the board. The second player then selects one of three options: play black, play white and place one more stone, or place two more stones to and let the first player choose the color. This is essentially a slightly more elaborate pie rule.
Tic-tac-toe Collection does not currently support the Swap2 rule, but it does support the pie rule.
Gomoku is an example of an m,n,k-game: either 15,15,5 or 19,19,5.