I use a ridiculous number of apps for writing stuff down digitally. It all depends on the context!
Rough notes, ideas and that sort of thing tend to be stored in Evernote. It’s easy, and ubiquitous and everything gets kept in one place.
Blog posts are written in MarsEdit, an offline editor. My local drafts folder is full of half-written, half-baked posts which occasionally get resurrected later on.
Proposals and other documents which I’m the only person likely to ever edit are done in Pages, and then exported to PDF for distribution. I just like the way Pages works in terms of laying things out and so on.
Documents and reports that I need to share in an editable format with colleagues or customers have to be written in Word. Since upgrading to the 2011 version on the Mac I have found myself getting angry much less!
Longer documents, such as various guides and handbooks I am working on tend to be planned using an outliner tool. My favourite at the moment is OmniOutliner.
I sometimes use a mind mapping tool to plan a document though, which is a bit more visual. My favourite mind mapping app is MindNode.
(As well as for documents, an outliner or mind mapper is really useful for planning presentations.)
For the actual writing of bigger documents, I use Scrivener. This lets you break down the document into smaller bits, which can then be dragged around and re-ordered. Scrivener then sticks it all together into one document for you when you’re ready to publish. It’s great!
Whether using OmniOutliner or MindNode, I can import my outlines into Scrivener by exporting them to an OPML file, which then loads into Scrivener, giving me all the headings under which I need to bash text.
What apps do you use for writing?