Here you can download Sudo Cue, a program that generates random Sudoku puzzles, allows you to enter puzzles manually, open and save puzzles in files, or use copy and paste to enter puzzles you can find on Sudoku forums. It has a variety of tools to help you solve even the most difficult puzzles. It can also solve puzzles and check whether they are valid. A variety of human-style solving techniques are used. These techniques produce an interactive log that helps you understand how they work.