Z-Write for Mac

From Stone Table Software:

Finally there's a word processor designed with writers in mind! Z-Write allows you to create an unlimited number of Sections and each Section can have as much or as little text as you'd like. You can create Sections for each of your main characters, with their biographies and other details neatly together. You could use Sections for individual Chapters, if you'd like. Whatever you do, Z-Write makes it easier to find and keep track of a huge amount of divergent material. Best of all, everything's preserved in a single file!