The goal of the FlightGear project is to create a sophisticated and open flight simulator framework for use in research or academic environments, pilot training, as an industry engineering tool, for DIY-ers to pursue their favorite interesting flight simulation idea, and last but certainly not least as a fun, realistic, and challenging desktop flight simulator. We are developing a sophisticated, open simulation framework that can be expanded and improved upon by anyone interested in contributing.
There are many exciting possibilities for an open, free flight sim. We hope that this project will be interesting and useful to many people in many areas. Source code for the entire project is available and licensed under the GNU General Public License.