A word processor with outline capabilities. A relatively simple word processor with extra features to support large creative writing projects. Features:
Margin Notes.
Automatic Outline
Full-screen mode
Database
Bookmarks
Separate formatting options for print and screen
It actually knows what a chapter is (or whatever organizational structure you want to use).
A panel for general notes lets you keep track of story issues and ideas (and the last time you ate).
Word count
More accurate page count estimates
Better performance than most word processors for really, really big documents.