Some websites to play tic-tac-toe online include Playtictactoe.org and NovelGames.com. While Playtictactoe.org tic-tac-toes feature one- and two-player game modes, NovelGames.com tic-tac-toes feature a multiplayer option in which users play against each other.
Tic-tac-toe is a game for two players who take turns to draw X's and O's on a three-by-three grid. The player who manages to place three of her symbols in a row either vertically, horizontally or diagonally wins the game. If no player can form a row, the game is a draw.
In 2013, Ben Orlin, the author of the Math blog MathWithBadDrawings.com, invented a variation of this game in which each of the nine squares of the grid is a tic-tac-toe game itself. The website CreativityGames.net features this variation of the game, which is called Ultimate Tic-tac-toe.