Instead of calling CrazyFlie (as it's known) a tiny quadcopter, it might be more accurate to just describe it as a PCB that happens to also be able to launch itself into the air. Measuring a scant 10 centimeters per side, CrazyFlie uses its PCB as a primary structural component, which helps keep the size and weight to a minimum... In total, we're talking about only 20 grams.
Despite its tinyness, the quadcopter includes a charging port, radio, 3-axis accelerometer, two gyroscopes, and a lightweight 110 mAh LiPO battery that gives it about four and a half minutes of flying time:
All of the data from the accelerometer and gyros is being used to keep the copter dynamically stable, making minuscule adjustments 250 times every second using the onboard CPU. And it seems to work pretty well: for such a little platform, CrazyFlie seems remarkably stable.
While CrazyFlie is handmade (and currently undergoing revisions and upgrades), it seems like it would be pretty cool to have something like this available in kit form. Who knows, it might even be possible to teach these little copters to work together to make giant displays, or even to perform a trick or two.