Tic Tac Toe is a two players game where players in turn mark the spaces is a 3×3 grid that represents the game board. The player that gets three marks in a horizontal, vertical or diagonal line wins the game.
Computationally speaking it is a very simple game with around 250,000 possible moves and it is possible to play a perfect game each time, that is, you can always win or draw if you are starting the the X.
So what make interesting this LEGO Tic Tac Toe robots?
The main interest is the fact that the robot moves the pieces itself which means they have to detect occupied tiles in the grid, to detect color and to move the robot arm so the piece can be placed correctly and with precision.
This other video is done using old Mindstorms RCX.