Mind Ninja is a simple abstract strategy game for 2 players.
It is unusual among board games in that the players themselves invent the win condition when the game starts, in a way that ensures both that equally-skilled players have equal chances to win, and that ties are impossible. This feature leads to great variety and depth of play.
The game is also a generalization of the the game of Hex, which means that the set of all possible ways that a game of Hex can play out is a subset of the set of all the possible ways a game of Mind Ninja can play out. Mind Ninja is a generalization of many other games as well, including Go-moku (5-in-a-row), Havannah, One-Capture Go, Y, Poly-Y, and *Star, among others.
It can be played with stones of two (or more) colors on any tiled surface. It can also be played with paper and colored markers. A version of the rules is available here.