Glance at the newsstands in your favorite magazine shop, and you'll likely see a sea of Sudoku books, each offering dozens of those wildly popular number puzzles. But you can save some cash by downloading a free Sudoku game for Windows PCs that also offers a few bells and whistles not found in its paper counterparts.

Pure Sudoku Free Edition contains 20,000 free puzzles -- enough for one a day for 54 years -- plus you get to choose from one of 43 unique backdrops to suit your mood. Need to get back to work? No problem, as you can save your puzzle progress and resume at a later time.

Whether you’re a novice Sudoku player or hardcore fan (or somewhere in the middle), this game offers four difficulty settings to suit your skill level. For the uninitiated, Sudoku (pronounced "su-doe-ku") challenges players to fill in all the blank squares on a 9x9 grid with the correct numbers -- but the catch is that each row and column must contain numbers 1 though 9, with no repeats. What's more, the nine 3x3 boxes that make up the grid must also contain numbers 1 through 9. Sudoku puzzles start with some numbers in the grid so you can begin the deduction process to fill in the rest.