From AHA! Software:
Whirlwords is based on the familiar pencil-and-paper word chain puzzles that require you to connect two words by a series of steps in which you change one letter at a time. Our version extends the concept by providing six types of transitions from one word to the next instead of only one. Whirlwords comes with more than 100 puzzles in order of increasing difficulty. It also features a nifty graphical interface, a built-in editor so that you can construct your own puzzles, complete on-line help, and a vocabulary of more than 5,000 words.