XO, also known as Tic Tac Toe, is a classic paper and pen game that is now available as an Android app. The game is played between two players, where one is X and the other is O. The players take turns to fill one of the squares that are formed by two vertical and two horizontal lines with either X or O. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game.

XO is a free game that is suitable for both kids and adults. It is a great way to challenge your brain and have fun at the same time. The app is easy to use and has a simple interface that allows you to play the game with ease. With XO, you can enjoy the classic game of Tic Tac Toe anytime and anywhere on your Android device for free.