In June we learned about a modification to the classic game of Tic-tac-toe that turned it from a game that experienced players would always end in a draw, to a genuinely challenging new game. But back then it was a game you could only play on paper, now it has become a fully-fledged app.Called Ultimate Tic-Tac-Toe, the iOS game has been developed by Wojciech Siudzinski and is available to purchase on the App Store for $1.99. It fully incorporates the ideas detailed in the original Ultimate game modifications and embeds a Tic-tac-toe board within each of the nine squares from the classic 2-player game.The rule changes also means your X or O placement is governed by where your opponent put his or her last mark. So if they put an X or O in the bottom left corner of a game board, your next move must occur in the bottom left board. This changes the gameplay significantly as you have to win the smaller boards in order to win the overall game. That means tactically managing the placement of marks across nine boards at the same time.Here’s a video of the Ultimate Tic-Tac-Toe app in action:I’d suggest trying out Ultimate Tic-tac-toe on paper with a friend before opting to spend $2 on an app. If you enjoy it, then the investment may be worth it if for no other reason than to save on paper and having to draw out the boards every time you want to play. The current version only supports 2 players via Game Center or locally, but an AI opponent is promised for v1.1.