Wikipedia
JSBSim
JSBSim is an open source Flight Dynamics Model (FDM) software library that models the flight dynamics of an aerospace vehicle. The library has been incorporated into the flight simulation packages FlightGear and OpenEaagles. It can also be called from a small standalone program to create a batch simulation tool. JSBSim has been in development and use since 1996, and has been built on all of the most popular platforms in use today including those running Linux, Macintosh, and Microsoft Windows operating systems. JSBSim is written in C++ and uses XML configuration files.