Euchre

Two people play tic-tac-toe on a three-by-three grid. Each player puts an X or an O in one of the nine spaces on the grid.
X won the tic-tac-toe game.
No one can agree on a rule for who plays first, but in this article, it is assumed that X plays first.
Players soon learn that if both sides play their best, the game will end in a draw. Because of this, tic-tac-toe is often played by young children who might not yet know the best way to play.
Because tic-tac-toe is so easy to play, it is often used as a teaching tool to teach good sportsmanship and the part of artificial intelligence called "finding the game tree." It is easy to write a computer program that can play tic-tac-toe perfectly or list 765 fundamental positions (complexity of state space) or 26,830 possible games (complexity of game tree) on this space, including rotations and reflections. Tic-tac-toe is a useless game because if both players play perfectly, the game always ends in a tie.