I use git for most of my writing (blog posts, content for my company's website, notes from meetings, journal entries about my kids, etc.) as well as for source code. Sort of a light-weight dropbox, with version control.

I've sometimes wondered (and perhaps this already exists, I've just never googled it) whether it would be useful to have a type of legal document that uses a markup suitable for revision tracking and version control. I find it's hard to be completely sure before signing a long legal document whether the version I've just received is precisely the same as the one my lawyer has reviewed.