WinSudoku is a Windows version of the famous game.

You can generate puzzles in sizes from 4x4 to 16x16 and difficulties from very easy to very hard. The Assistant can help you with scanning, markup and revealing certain numbers, allowing you to focus on the logic. Puzzles can be printed out on paper, stored for later use and saved as an image. You can also solve newspaper puzzles. Ability to select color theme.