The thing to remember about Plots Unlimited is that, even though it may look like it's writing a complete professional story for you, it isn't unique. Although Aristotle probably never envisioned his works being used to create a salable screenplay, Collaborator's source material has certainly stood the test of time and is arguably the least controversial foundation of any story development software evaluated. Collaborator steps you through a series of about 70 questions designed to make you think deliberately about your story and, more importantly, to ask the right questions about your story. Although the questions are presented in an order which builds from the general to the specific, you're free to leap around like a march hare if the moody muse strikes you. The questions are answered in free-form text, some of which are plugged into other questions by the program.
Collaborator is the program most subject to the old saw.
You get out what you put in. While the other programs force you to think differently about your story by the simple act of working with their unique interfaces. Collaborator is sufficiently straightforward that you can sleepwalk through it. If you don't apply your creative energies seriously, Collaborator will leave you with a collection of half-baked musings no better realized than the pliant recapitulations of an apathetic writing partner. StoryLine Pro offers a collection of interconnected tools to help writers develop solid stories.