SudoKoach Description:

SudoKoach makes solving Sudoku puzzles more fun. It does the tedious work of figuring which numbers are possible in each unsolved cell, so you can concentrate on the more interesting patterns of solving the puzzle.
Solving Sudoku puzzles with SudoKoach is more fun because:

You don't have to figure out which numbers are possible in each cell.
There is no need to write down and constantly update these possibilities.
You can check any time to see whether you've made any mistakes.
If you make a mistake you can easily undo your moves.
You can resize the window to make the grid as large as you want--no more squinting!
If you get stuck, you can get hints to get you going again.
You can create as many puzzles as you want, with six different levels of difficulty.
You can enter puzzles you've found elsewhere and solve them too.
You can print puzzles (with or without showing the possibilities) for later solving, or to give to friends.
You can practice any of the solving strategies to improve your skill.