This is a pretty advanced implementation of a Sudoku puzzle generator. It allows multiple Undo. If you are on the right track (haven't made moves that make it impossible for the program to solve), you can ask the program to generate the solution to any puzzle. Choose from different levels of difficulty. This is my big entry for N.A.N.Y. 2014. Couple thousand lines of code, bit of a headache.
Download link: http://kyrathaba.dcmembers.com/ccount/click.php?id=22
Requires .NET Framework installed.
Downloads (as of 02/22/2014): 157