The Invisible Train
Digital_Quartz writes "Students at the Vienna University of Technology have come up with an augmented reality game in which players control virtual trains on a real wooden track. Players can adjust railway switches, and must prevent the trains from colliding. The catch is, of course, that the trains don't exist; they are viewed and controlled using networked PDAs with cameras. The system is based on the custom Studierstube framework for creating augmented reality applications for handhelds."
This was on display in the "Emerging Technologies" display at Siggraph in August 2004 in Los Angeles. The display was quite popular, though I did not try it. But a lot of people should have more to say about it than I have seen here so far...