Sudoku Easy to Hard Puzzles HD is a highly rated app (or website) that provides users with hundreds of different Sudoku puzzles of varying levels of difficulty. It features over 500 puzzles ranging from easy to hard, with more puzzles added daily. The puzzles can be played on a variety of devices and the app also offers an integrated timer so you can track your progress and compete with friends. The game offers a variety of customization options including game board size and color, and the ability to switch between different difficulty levels. The app also includes a tutorial which explains the rules of Sudoku and provides helpful hints and tips.
Discontinued It seems that the project is no longer updated, but the latest version, 2.2.0, released in July 2012, is fully functional and can still be downloaded from the official website.