Scrivener is an excellent word processor for long-form writing in particular. It was designed from the ground up with writing efficiency in mind, and harkens back to the golden age of word processing when we had speedy and versatile tools like Wordstar, WordPerfect, Textra (my favorite!), etc. It's currently 50% off at Amazon - $20.
Not sure how long the sale will last, so get it soon.
If you're not familiar with it, hop over to the Literature and Latte site, download a free copy, and do a quick trial of it first.
My only complaint about Scrivener is that there's no GNU/Linux version.