Gomoku
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. Because pieces are not moved or removed from the board, Gomoku may also be played as a paper-and-pencil game. The game is known in several countries under different names.
Rules of Go
In the first diagram below, it is White's turn. White must prevent Black from connecting the marked stones to the others by playing at "a". The second diagram shows White's move. White is threatening to kill the marked black stones by playing at "b". In the third diagram, Black plays at "b" to prevent this, capturing White 1. However, by playing at "a" again, White can capture Black 2's group. This is not barred by the ko rule because the resulting position, shown in the fourth diagram, differs from the one after White 1 by the absence of the marked black stones. This kind of capture is called a "snapback".