ARTag
Ten holy craps, that’s cool.
You put a little 2d barcode sticker on something and this software recognizes it.
Then you can do anything with the graphic output: label parts in a car as you look at them in context to what you’re fixing, have peoples’ homepages float over their heads, find a book on your shelf instantly, leave comprehensive notes — books, even — about places, attach URLs to any object you own…
Awesome