Sudoku is a logic-based, combinatorial number-placement puzzle. The puzzle was popularized in 1986 by the Japanese puzzle company Nikoli, under the name Sudoku, meaning single number.

The objective is to fill an N×N grid with digits (1 to N) such that each row, column and block contains only one occurrence of each available digit. Some squares are pre-filled as clues; place the rest of the digits correctly until the grid is complete.

The default puzzle mode is 3x3; (actually a 9x9 grid, divided into nine 3x3 blocks). There are also modes with rectangular blocks rather than square ones. An alternative 'jigsaw' mode, with arbitrary shaped blocks. Plus a 'killer' mode, where rather than clues in the form of filled squares, you're given cages with a clue noting the sum of the digits within the cage. (No number may appear more than once in a cage; even if the cage crosses into another block).

The game supports 14 modes of play on iPhone, iPod Touch & iPad; plus GameCenter integration, so you can beat your friends' best times. Oh...and the puzzles are auto generated...so no in-app-purchases necessary!