Yup, it’s only for MACs. Here’s the link: http://www.literatureandlatte.com/scrivener.html Well worth going out and buying a MAC just so you can have Scrivener. It was written up in the NYT a few weeks ago. I’ve owned it for about a year now and I can’t imagine writing without it. Take a look.
The developer, Keith, is an absolute angel and a real class act.
(Edited to fix the link)