Plot Control, from Reelwriting.com, is a screenwriting aid that helps organize and fleshout your screenplay. When I heard about the program I was intrigued. Screenplays are created by answering a series of questions and building on those. When you finish, you'll have a well thought out proposal without a lot of holes in the story, and you can see how the pieces fit together at a quick glance. Another nice feature, are the videos that explain plot and storyline. That was another big plus for me. I've never tried screenwriting before, and I can see how this program is a big help.
Their support is prompt and friendly. I keep having licensing problems after running a cleaner program. A short email to support, and they had me up and goming withing a few minutes.
Reelwriting offers a free trial, so they're willing to let you decide if Plot Control will fill you needs.
Youtube has a video showing the program, and some of it's many feature.