Sudoku
How to play Sudoku
Sudoku is game that originated in the East. It is a puzzle game that requires the solver to place numbers from 1 to 9 in a certain way. The playing board contains nine rows and nine columns to form a nine by nine matrix of number positions. The playing board is further divided into blocks of 3 x 3 number positions. The object of the puzzle is to place the numbers, 1 to 9, so that there is no repeat numbers in each: row, column and box. The order of the numbers is not important, just that each number only appear once in each of the row, column and boxes.
http://www.puzzle.jp/letsplay/sudokuruleflash-e.html