From 9to5Toys Specials:
If you’re serious about writing, Scrivener is a great investment. Used by many bestselling authors, this wordsmith’s toolbox is currently $22.50 for Mac
Unlike your regular office suite, Scrivener is set up for long-form and creative writing. Along with the “snapshots” feature — each major version of your draft can be restored — the app features a storyboard tool, and a database for collecting relevant notes.
An outliner tool is also included to help you shape your narrative, and you can place research documents in floating windows for easy reference. Scriptwriting is made smoother thanks to the custom formatting options, and the clean full-screen mode is great for staying focused. The desktop app syncs with the mobile versions of Scrivener, too.