FlightGear is a collaborative project that aims to create a sophisticated free software flight simulator framework. It is licensed under the GNU GPL and runs on multiple platforms and operating systems, for example Microsoft Windows (Win9x/ME/2000/XP), Linux, Mac OS X and Unix.

The simulation engine in FlightGear is called SimGear. It is used both as an end-user application and in academic and research environments, for the development and pursuit of flight simulation ideas.

This customizability of the game is illustrated by the wide range of aircraft models that are available in FlightGear, from gliders to helicopters, and from airliners to fighter jets. These aircraft models have been contributed by many different people.