It seems that when most people think of virtual reality games, they envision some schmuck in clunky headgear "running" through a Quake-style world shooting at monsters and having sex with cartoons. It's hard to blame them; We've all seen this style of VR at various theme parks and shopping malls (maybe the sex with cartoons was just me). Unfortunately, they don't really live up to the hype - the only thing virtual about them is the fun you virtually have while playing, and the sober reality of paying $5.00 for five minutes of this nonsense. The next generation, presuming it ever crawls out of research labs and into our homes (and malls), promises a much more interesting experience via Augmented Reality (AR), which differs from virtual reality primarily by virtue of the fact that you don't wear goggles. The Invisible Train is an excellent example of this.
The Invisible Train isn't merely invisible; it doesn't exist in reality at all. The wooden track exists, and its modular nature allows for virtually infinite track designs; the train, on the other hand, exists only within your PDA. You control the train and the track switching with your stylus, while you and your buddy watch the action unfold on the display. The object of the game at this point is simply to keep the trains from running into each other, but the potential for more complex and involved game modes in the future is clear.
It's like your PDA is a "magic mirror" into fantastic world where trains really do exist.