Sudoku solver is simple Javascript solver. Although much faster algorithms exist, not sure that all of them are ported to Javascript yet. For more information on the Sudoku algorithms, see the Wiki page.
To use this solver, you may input puzzle in the 9x9 grid, and then click the `Solve' button. Alternatively, you may select predefined puzzles to fill the grid or write the puzzle string in URL, for example like this.