Hashiwokakero
Hashiwokakero, or Bridges, is a sudoku-like logic puzzle in which you have to connect all the islands with the number of bridges specified on each island. They have to go in straight horizontal or vertical lines, and you get a maximum of two bridges between any two islands. The solution must also be connected; that is, there has to be a path over the bridges from any island to any other island. For a sample solution, see the FAQ.
You create a bridge by clicking on one island and dragging to another, and a second bridge the same way. If you try to do a third bridge, you go back to zero bridges. You don’t actually have to drag all the way to the second island, just a little ways in one of the four possible directions. Click the Ready button to check your progress.
Now you’re addicted, too!