FlightGear Flight Simulator is a mature, sophisticated, open-source flight simulator software package, created and maintained entirely by volunteers. The complete project source code is available via CVS, freely licensed under the GNU General Public License. FlightGear version 1.9.1 was released on the 25th of January 2009.
The goals of the FlightGear project include creating a sophisticated flight simulator framework for use in research or academic environments, for the development and pursuit of other interesting flight simulation ideas, and as an end-user application. It can be expanded and improved upon by anyone interested in contributing, and has many related projects (projects).
FlightGear comes with a set of illustrated documentation, notably "The Manual", which is available as PDF and HTML. The FlightGear Wiki was started in 2006 and currently covers a wide range of FlightGear related topics.