They belong to a class of flying machines called quadcopters – made only possible with recent advances in MEMS electronics (specifically, accelerometers, electronic gyros, and microprocessors). These are classic examples of fly-by-wire machines where a computer evaluates the flying conditions thousands of times per second and provides mid-course corrections, while a human pilot tells the computer where he or she wants to go.

http://aeroquad.info/bin/view
- an Arduino-based quad-copter, built from Align 600-series helicopter tail booms, brushless motors and propellers. An Align T-Rex600′s landing skid provides lander support.

http://quaduino.org/
- Another Arduino quad copter. Looks like a custom airframe.