A free program for Android, by Logic-Wiz.

Classic Sudoku by Logic Wiz is a great logic game. It offers a lot of challenges that will keep you playing for hours.

It is divided into 5 levels: Beginner, Easy, Medium, Difficult, Expert.

The app has an interface that is very easy to use. You will find the game tools on the top left side.

On the top right, you will find the 3 buttons: Undo, Hint, and Show Error.

The hints will help you to solve the puzzles. The undo button will let you change the move you made. The show error button will show the error that you made.

There is also a table of all the possible moves.