MAVLink is a very lightweight, header-only message marshalling library for communicating with micro air vehicles. MAVLink was first released early 2009 by Lorenz Meier under a GPL license. The MAVLINK Common Message Set describes the various message headers. You can integrate MAVLink with the Robot Operating System (ROS) in order to control your micro air vehicle.
QGroundControl, the open source Micro Air Vehicle Ground Control Station / Operator Control Unit can be used to operate your Drone. It is based on PIXHAWK’s Groundstation. Further development is now done in a joint effort with the community. Have a look a the QGroundControl video to get an idea of its control interface.