Kakuro is the next puzzle taking over the world in a storm like sudoku did.* it is considered more challanging and it requires basic adding and substracting skills.
All of our puzzles have only one solution AND all the puzzles can be solved logically without need of guessing.
What's great about it is that every puzzle can look different, in it's size and in it's shape.
I programmed it myself, let me know if you have any comments :-)
Here it is :
http://www.kakurolive.com