Killer Sudoku (aka Sumdoku) is a Sudoku variant where cells are grouped into cages and the sums of the values in each cage are given. It's much more fun than normal Sudoku :).

App includes 16 4x4 and 36 6x6 puzzles for beginners and hundreds of 8x8 and 9x9 puzzles with varying degrees of difficulty for advanced users and expert solvers. Plus a sum calculator to help you figure out possible matches and ability to validate progress.