Sudoku Susser
Sudoku Susser is a specialized program that helps you solve Sudoku puzzle games. It gives you full, interactive control over the solving process and explains what it's doing every step of the way. It can provide hints, solve the puzzle by human deductive reasoning or brute-force recursion, and a variety of hilighting modes help you see the patterns in a puzzle. It also enables you to drag Sudoku graphics from any webpage, and it will scan them and load them into the program for you.
Sudoku Susser features a graphical representation of all remaining possibilities for each cell, and it will highlight the valid squares (as well as show the ones that cannot be valid) in different ways. It can even display the possible combinations of numbers in a box or in each individual column and row, which is especially useful when you are trying to find a 'hidden' number. It can also hilight over a dozen different simple and advanced Sudoku patterns, ranging from forces and pins to mega-expert techniques like forcing chains and nishio.
This program is designed by Sudoku enthusiasts for Sudoku enthusiasts, and it has everything a Sudoku fan would want in a Sudoku software application. It can copy/paste puzzles directly from newspapers, and it will also let you generate your own. It has unlimited undo/redo for reversing square allocations, and it allows you to print out a Sudoku puzzle for manual solving. It has a full range of information about Sudoku, including message boards.