Killer Sudoku

Killer Sudoku (aka Sumdoku / Mathdoku) is a Sudoku variant where cells are grouped into cages and the sums of the values in each cage are given. Once you know Killer, you will never go back to Classic again...

The app includes lots of cute little 4x4 and 6x6 puzzles, perfect for beginners, with contextual hints to help you learn Killer techniques interactively. From there you graduate to 23 levels of chunky 8x8 and full-size 9x9 puzzles, guaranteed to stretch any brain. Are you one of the very few who can conquer 9x9 level 15???

The app has everything you could wish for: gazillions of puzzles at all sizes and levels, automatic notes, drag copy & repeat entries, sum calculator, cage summer, progress validator, and hints.