By now, everyone knows about Sudoku, but what about Kakuro and Spidoku? Kakuro involves fitting numbers into rows and columns, each of which must add up to a different specified total. You won't have heard of Spidoku, because it's only just been invented. Here you have to insert the numbers one to eight into the rings and segments of a shape like a spider's web, without repeating any digit. You can find them all in a paperback called Kidoku. As the name suggests, it's for children but some adults will probably steal their copy. Kidoku is published by Wizard Books at pound;4.99.