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). The full version of this app also has 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, youre 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).
This lite version supports 8 modes of play on iPhone, iPod Touch & iPad. Oh...and the puzzles are auto generated...so no in-app-purchases necessary!