FlightGear is a free and open source Flight Simulator for Linux, Windows, Mac OS-X, FreeBSD, Solaris, and IRIX. FlightGear Flight Simulator comes with 3 primary Flight Dynamics Models and you can also add new dynamics models. Available Flight Dynamics Models are JSBSim, YASim and UIUC. It support standard 3d model formats and xml based ascii files. Some of the important features are more than 20000 real world airports, Sloping runways, accurate and detailed terrain and sky model like lakes, rivers, roads, railroads, cities, towns, sun, moon and stars.