Odd

Odd is a simple abstract game for 2 players, with stones of 2 colors, typically played on a hexagonally tiled board with 5 cells on each edge (though it can be played on almost any tiling). Odd can also be played with pencil and paper.

Definitions:

 A group is a set of stones on the board, all of the same color, for which it is possible to trace a continuous path between any two of  them by stepping between adjacent stones of that color.
 The size of a group is the number of stones in it.  

Rules:

 The board begins empty.
 Players take turns.  On each turn a player places one stone of either color onto any empty space.
 The game ends when the board is full.  Player 1 wins if there is an odd number of groups of at least size 5 on the board, and Player 2 wins otherwise.  When counting groups, be sure add up the total number of connected groups of both colors.

Notes:

 One can change the character of the game by increasing or decreasing the minimum size which a group must have in order to be counted at the end. The larger the minimum group size, the more strategic and less tactical the game becomes, and vice-versa