When you enter a word into Visuwords, it creates a graphical abstract of all related terms, and ties them together in a web that you can manipulate. Mousing over a term defines it, and you can drag the terms around, into groups, or stretch the web apart to see how related terms relate to each other. It is, as the kids say, mad cool. You can see it in action at visuwords.com
Thanks to Tom Barrett for the initial information on this in his del.iciou.us links.