From Tatsuhiro Nishioka:
FlightGear Flight Simulator is an open-source flight simulator created by the FlightGear project. Source code for the entire project is available from a CVS repository and licensed under GNU General Public License (GPL). FlightGear 1.0 was released in December 2007 (v1.0 Gallery). FlightGear has been in the midst of a software architecture transition from PLIB to OSG. 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. This version is the first release on CNET Download.com.