Scrivener is an excellent, idiosyncratic app for creating and managing complex writing projects, whether you're trying to write a novel, play, TV show, or magazine feature. No simple word processor, Scrivener is a full authoring tool, using a metaphorical "three-ring binder" interface that helps you organize draft text and research documents into a simple system for writing, revising, and rearranging text.
While the basics of Scrivener's interface are intuitive--the system of folders, documents, and index cards on a virtual corkboard--you'll need to invest some time and effort to fully understand all of its features, including flexible output options, "snapshots" for handling revisions, a potent outlining tool, full-screen editing mode, and an exhaustive system for keywords, labels, and the like. Thankfully, Scrivener has a feature-summary video, a built-in tutorial, a responsive developer, and an active and enthusiastic user community. Scrivener also now supports a couple of new formats--Final Draft's FDX and Write Room's WS--so you can easily move files from those applications. The price tag might seem steep given the ubiquity of free and cheap text editors, but Scrivener is an exceptional tool built for a particular task.