OpenSudoku is a free and open source mobile game that is available for Android and iOS devices. The objective of the game is to fill a 9x9 grid with digits from 1 to 9 so that each column, row and 3x3 box contains all digits from 1 to 9. The game starts with some of the grid squares filled with digits and the player has to fill in the remaining squares. The player can choose from four difficulty levels ranging from easy to hard. The game also features unlimited undo and redo, hints and an auto-save feature. The game also includes support for multiple languages and themes, as well as a leaderboard and achievements. OpenSudoku is a great way to relax and pass the time while exercising your brain.
Discontinued It seems that the project is no longer updated, but the latest version, 2.2.0, released in July 2012, is fully working and can still be downloaded from the official website.