Originally created in 2008 as a simultaneous web game and Facebook application, Sudoku Fighter is a multiplayer Sudoku game where users race against each other to complete puzzles. During each battle, the system tracks and displays opponent grids to each player (replacing the other player's numbers with filled in squares) to help heighten the intensity.

It took about 3 months of spare time to complete the multiplayer mode as a Facebook application, and in that time several similar competing games had launched. The project was then abandoned but later picked up in 2011 and completed/launched as a fully functional website. The Facebook application portion was removed and the following features were added: User profiles, Singleplayer mode, Player stat tracking, Player taunts, Puzzle voting.

The site is still operational but registration is closed until some cobwebs are cleared out. Given that William seems to work on this project once every 3 years, perhaps you'll see an update in 2014!

Both the website and Facebook application were taken offline in 2013.