PentPakFree

This is a fun and mind challenging alternative to Sudoku. This app give you one puzzle to learn the rules and try it out. If you like it then you can purchase PentPak01 which gives you 30 puzzles. You'll find it addictive (in a good way) and a way to expand your thinking. If you are not fond of numbers you can switch to a letter mode that displays letters instead of numbers. You cross word puzzle fans might really enjoy this if the number-centric approach of Sudoko has put you off.