I'm not a big fan of writing software in general (other than formatting programs for writing scripts) but there is a new program that looks intriguing. It's for Mac users (for a change...) and is called Avenir. Here's what their blurb says:
"Avenir is a new kind of software for writers. Part word processor, part database, completely focused on the creative process. Whether you are brainstorming for your first short story or putting the finishing touches on your latest best-seller Avenir provides the tools you need to manage the creative process from inception to publication.
You can track, tag and filter characters, scenes, locations, research and more with the unique dynamic outline. It even provides special tools for fiction writers like word frequency counting and a progress meter to help you meet your daily writing goal."
This is not an endorsement, I've just downloaded it for a free 30-day trial and eventually I'll come back with a review--but I thought you might be interested in trying it for yourself. The free trial version is available for download here.