I use Write It Now. Honestly if Scrivener had a Windows version I would most likely use it instead; Write It Now has several unattractive quirks.
What it does have, though, are some very useful features. Storyboard, for example. I suggest writers find some way to use this or a similar tool, because it is such a help. Especially if you write by the seat of your pants like I do. It's a bit terrifying to see all of my effort laid out like that.
Quote of the day from the second revision of Sacrificial Magic:
"Fury. An agony that lived in the heart rather than in the body. The painful, scourging power of revelation. He looked beyond, in to the realm of all that was good and holy, and lifted his sword."