is open source autopilot hardware and software for radio controlled planes. It is based on the Parallax Propeller microcontroller, and uses a 5-degrees-of-freedom IMU plus a GPS and proximity sensor to stabilize and navigate your plane.
It can be enabled/disabled through an extra channel/switch on your transmitter, and when switched on, stabilizes the plane and navigates it back to the starting location, where it will circle. It can also optionally trigger external actions, like taking a photo or dropping an item, when it reaches a waypoint.
Coming soon: multiple waypoints, stabilization of inverted flight, on-board TV-out, and more.
If you're interested in helping out, there's lots to be done! Swing on over to the project page and join the octopilot group.