The ArduPilot Mega 2.5 is a complete open source autopilot system. It allows the user to turn any fixed, rotary wing or multirotor vehicle (even cars and boats) into a fully autonomous vehicle; capable of performing programmed GPS missions with waypoints.
Onboard Dataflash chip.
Digital compass powered by Honeywell's HMC5883L-TR chip, now included on the main board.
Optional off-board GPS, Mediatek MT3329 or uBlox LEA-6H module.
One of the first open source autopilot systems to use Invensense's 6 DoF Accelerometer/Gyro MPU-6000.
Barometric pressure sensor upgraded to MS5611-01BA03, from Measurement Specialties.
Atmel's ATMEGA2560 and ATMEGA32U-2 chips for processing and usb functions respectively.