Scrivener (Mac only) is a word processor specifically designed for writers. It doesn’t do some things that a major word processor like Microsoft Word does. Instead, it focuses on the tasks that writers need and takes them to the next level. It provides a “corkboard” where you can “storyboard” your book using virtual index cards. If you want a more traditional approach, it provides a fully-featured outliner. My favorite aspect of the program is full-screen editing. You can eliminate all the distractions of other programs and windows and focus on the single document you are working right now. You can try the program free for 30-days. The purchase price is only $39.95. I would start by watching this video.