For years I've been looking for a word processor that is actually made for writing novels. Something that lets you work in chapters and rearrange those chapters easily with a drag-and-drop pallet.
Scrivener changes all that. Not only does it think in chapters, you can rearrange them and attach notes and comments that stay with the chapters. It also let's you divide your work into parts and sections.
Scrivener is more of writing studio than a word processor. With templates you can use for all sorts of long-form writing that require research, copious notes or world building.
It is very customizable, almost too customizable some complain, as it may take awhile to get set to your liking. However, I found it useful right out of the box for the ability to drag & drop chapters alone. And at only $49, it is an unbelievable bargain as well.
I still use Final Draft for screenplays, although Scrivener does have template for screen and playwriting and many use it as an alternative to Final Draft.
Where Scrivener shines is in editing and doing rewrites. We could leave comments for each other during the second draft phase, move chapters around with ease and keep track of multiple story arcs.
But most of all, Scrivener lets you write. You don't worry about formatting until you are ready to send off the manuscript or publish it as an eBook. "The Compiler," outputs you document in a variety of formats. I have the novel template loaded, but there are templates for non-fiction as well. An online community makes and trades templates for just about any format you can think of, and it is fairly easy to create your own custom templates.