What? You don't have a Sphero? Well, you're going to need one to play this amusing free game. Sphero is a neat little ball-shaped robot that rolls around in response to things going on inside your phone. In this case it rolls around your floor killing augmented reality zombies with fireballs. That's got pretty much all the makings of something awesome.
So you point your device's camera at the Sphero, and the undead will attack. As you guide your sphere of death around in real life, the virtual zombies respond to it. You can play the game anyplace there is a flat enough surface for the Sphero to roll around on.
There are a number of other Sphero apps, but the device itself is $99 (down from $130). Kidding aside, this one does actually look kind of compelling.