I've been fiddling around with Google Groups recently to communicate with my Roleplaying Game Group (Yes, i'm that kind of geek). I've been finding it very useful, and noticing one of the really nice hidden features: the "Page" editor. This page editor is basically a slimple CMS based on a standard "Rich Text Editor" sort of interface, but it's very powerful for my small group to be able to document things without going through the trouble of a full blown Word/OpenOffice/RTF document, or trying to link in a Google Docs Document.
Expanding beyond my current use, I can see it being very useful for a small development group to store API Docs, Design Docs, Requirements, etc. Yeah, there are more powerful tools available, but this one works really well, and has just the sort of versioning capabilities that are useful without being obtrusive.