Sudoku is a Japanese number game that's taking the world by storm. "Sudoku" (数独), actually a trademarked name, is the shortened form of the phrase "numbers (数字) for when you're alone (独身)." In other words, sudoku is a great time-killer.
Sudoku will either mellow you out, or drive you mad. To see which category you fall into, you can try playing online here.