Subplot is a story-planning system for novelists and screenwriters. Use Subplot to keep track of Who, What, Where, When, and Why in your writing projects.
Subplot is designed to be used alongside your existing writing tool or word-processor. You don't write your story in Subplot, instead you use Subplot to keep track of what you need to do next.
Have you just added a killer red herring to your murder mystery? Now you need to go back and add details about it to your story. With Subplot, you can easily add your red herring to the relevant scenes in your plan and use Subplot's reports to judge whether you've given the reader enough opportunities to put the pieces together.
Subplot won't tell you how or what to write, but you can use it to keep yourself on the path to completing your project.