There's a game where you try to turn one word into another by changing only one letter at a time. Letters can be added, removed, or changed in place, but all intermediate steps must be real words. For example, you can get from "cat" to "dog" by doing "cat, cot, dot, dog".
This applet solves the game for any pair of words. It uses a breadth-first search to find one of the shortest possible solutions.