John’s Sudoku :)

John's Sudoku is one of the most comprehensive Sudoku game systems. It randomly creates puzzles of six difficulty levels. You may never encounter the same puzzle. However, you can do the same puzzle with user-defined puzzles. Or you can define your own puzzles from Sudoku books. You can also share the same puzzle with your friends through the input/output function of this system. The features are summarized as follows:
1. Randomly generate puzzles of six difficulty levels.
2. Users can define their own puzzles, such as from Sudoku books.
3. Check the status and highlight errors.
4. Use the most advanced highlighting function to easily view the working cells.
5. Automatically mark the selected cells.
6. Undo/redo function.
7. One-key automatic marking (or erasing) of all cells.
8. Can return to the previous correct state by 'eliminating incorrect entries'.
9. Puzzle-solving function.
10. Share the fun with friends by inputting/outputting puzzles.
11. Reset to the original puzzle.
12. The game is automatically saved and you just need to click "Restore".