A program that can solve sudokus of all sizes and lets you play around with sudokus.
The latest versions include a graphical user interface that lets you play sudoku games yourself. By right-clicking on a cell you can set this cell manually and step by step solve the whole sudoku. The Sudoku Solver helps you with that by providing the options to undo your last changes and by giving you suggestions if you are stuck. If you filled the whole sudoku, the application tells you whether you solved the sudoku or produced an invalid board. You can also let the application solve the sudoku completely for you if you want.
Of course this works for sudokus of all sizes, here are some examples:
