I’ve been reading through Tracy Fullerton’s Game Design Workshop, and one of the exercises is to extend Tic-Tac-Toe to three players. One of the least satisfying aspects of Tic-Tac-Toe is its predictable outcome (a tie), so I decided to let the third player shake things up a bit by shifting the board left, right, up, or down.
Find two friends and give it a try. Just like the original, players O and X win by completing a line. Player + wins by forcing a tie.