A new augmented reality app called Layar is making the rounds on the web as an example of what can be done with Augmented Reality. Layer (via 9to5Mac) is described as the world's first mobile augmented reailty browser.
The app accomplishes this through the use of the Compass, camera and GPS embedded within the phone. The developer's video shows it running:Layar shows you what is around you by displaying realtime digital information on top of reality through the camera of the mobile phone. Just flip through the directory of layers and find ATM's, bars, houses for sale, hotels and other cool stuff around you.
Article Link: 'Layar' Shows Augmented Reality Possibilities on iPhone 3G S
The app is first available for the Android devices but they are working hard on porting it to other platforms "with a prime focus on the iPhone 3G S.". The iPhone 3G S is the first Apple iPhone to contain a digital compass which is required for such applications.