Copyright (c) 1965 Universal Games, Inc.

Gambit is played on a 9x11 square board with the following setup (I'm not 100% sure if it's the right one):

TURN - On each turn, each player moves one of his stones to an (orthogonal) adjacent empty cell.
After a move, if an orthogonal line of friendly pieces is next to an orthogonal line of enemy pieces, the player with the longer line captures the other line. 
The King counts as two pieces.
GOAL - Wins the player that captures the opponent King or captures all the soldiers.
An example

If it is Black's turn, he should play f1 to f2, making a line of strength 3 (the King is worth 2) capturing the green line with strength 2 (i.e., the soldiers f4 and f5).

If it is Green's turn, he should move his King south to f6, making a line with strength 4, capturing the opponent King and thus, winning the game.

The column capturing is similar to Epaminondas, but Gambit's move mechanics makes it a much slower game.