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.
FlightGear is an open-source project. This means as long as you abide by the terms of the GPL license you may freely download and copy FlightGear. Anyway can have easy and open access to the latest development source code. Being an open-source project, we have made our file formats open and easily accessible. We support standard 3d model formats and much of the simulator configuration is controlled through xml based ascii files. Writing 3rd party extensions for FlightGear (or even directly modifying the FlightGear source code) is straightforward and doesn't require a large amount of reverse engineering. This makes FlightGear an attractive option for use in private, commercial, research, or hobby projects.
FlightGear is known to run on Windows, Linux, Mac OS-X, FreeBSD, Solaris, and IRIX platforms allowing the user run on their platform of preference.
Please go to flightgear for more detail.
youcan download from author here :