You know people do those 2D and 3D plots with dots representing where ideas are on a spectrum? You know, like this: http://www.politicalcompass.org/images/axeswithnames.gif

I think what you need is a diagram like that with Google Docs, Wikis, Evernote, Piratepad, E-mail and your product. You know, something that answers every "so how's it different from" at the same time.