Writer.app is a simple word processor. It's designed to get your first draft banged out and on its way to the editing table. Which is a prefect complement to NaNoWriMo, if you're into that sort of thing. So get writing. Well, download it first. Then get started. Make sure you have your coffee or tea made already, so you have no more excuses.
Version 1.4.3: A few cosmetic changes to toolbar icons, and pressing delete twice in a row will delete the previous word (which could just be the full stop, or other punctuation mark).
Mac OS X 10.4 or later (meaning it hasn't been tested on anything earlier, though it *may* work on 10.3)