http://toucharcade.com/2010/09/29/ardefender-augmented-reality-defense-game-now-available/
"Just two days after we took a hands-on look at ARDefender from developer Int13, the game has now become available in the App Store as of this morning. What is a nice surprise is that the game has launched for just 99¢. In ARDefender, you'll print out a special PDF image from ARDefender.com that is read by the software and creates a 3D tower in the real-life space of the iOS device camera's view. Enemies then attack the tower from all angles, and you fend them off with a weapon placed on top of the tower. You'll have a machine gun, rockets, and a laser at your disposal as you take on the endless waves of increasingly difficult enemies.
"It's a cool concept and one that works really well in practice. I was blown away with how convincingly the tower seems to actually exist in the area where you're playing the game...."
