Take a step back in time.. The latest update in the Augmented Reality development world! Philadelphia has mapped out their archive on phillyhistory.org of over 90,000 geocoded images and developed an app, where you can walk around the streets and see what it was like through the ages!
You can read about how they achieved this first stage effort in their online white paper here and the prototype Augmented Reality by PhillyHistory.org application will remain available for download until July 2011.
Pretty amazing stuff! :)