Sudoku (数独) is the number placing game taking the world by storm.

The rules of Sudoku are simple. Enter digits from 1 to 9 into the blank spaces. Every row must contain one of each digit. So must every column, as must every 3x3 square.

Each Sudoku has a unique solution that can be reached logically without guessing.

One nice feature of this site is that it clocks you and provides feedback on your performance, plotting your time to completion within the distribution of all players.