A game published in the 1960s by the 3M corporation in their "bookshelf" line. The board consists of a 24x24 array of holes arranged in a square grid. The outermost line of holes surrounding the board is partitioned off, and opposite sides are assigned to opposing players by colors red and black (similarly to Hex).
Players take turns placing colored pegs into the holes, and when two pegs of the same color share a "Knight's Move" relationship to each other, they place a small plastic bar across the tops of the pegs. As in Hex, the goal is to complete a bridge from one side of the board to the opposite side using these bars. Since bars are not allowed to cross each other, they can be used defensively as well.