FlightGear Flight Simulator (often shortened to FlightGear or FGFS) is a free, open source multi-platform flight simulator developed by the FlightGear project since 1997.

David Murr started the project on April 8, 1996. The project had its first release in 1997 and continued in development. It has specific builds for a variety of operating systems including Microsoft Windows, macOS, Linux, IRIX, and Solaris.

FlightGear is an atmospheric and orbital flight simulator used in aerospace research and industry. Its flight dynamics engine (JSBSim) is used in a 2015 NASA benchmark to judge new simulation code to the standards of the space industry.