Kakuro, the next puzzle after sudoku is taking over the world in a storm. Kakuro is like a crosswords with numbers, it is considered more challanging than sudoku, it required basic adding and substracting skills and what's great about it is that every puzzle can look differend, in it's size and in it's shape.
This group will discuss Kakuro and provide links for related webpages, i think that currently Kakurolive provides the best option to play kakuro online.