I'm working on a revision control system for spreadsheets (http://www.spreadgit.com) so people can sort out their Excel mess, ie. track changes, diff and eventually merge versions like you'd do with code.
A while back I tried brainstorming a bunch of revision control for <x>'s. I figured there were plenty of industries outside of programming that could use a tailor-made versioning system. Later on, I ran across one of them at https://layervault.com/ which is for graphic designers, which seemed (to me at least) to prove that the more general concept has legs.