FlightGear is a free open source flight simulator which was created out of frustration with the existing major flight simulators. FlightGear is a realistic flight simulator with ability to extend it with addons.

FlightGear has many features you would expect to find in a commercial flight simulator and with the advantage of being available across multiple platforms. There are also many add ons available, such as more aircraft like the Wright brothers original plane and over 20,000 real airports if you download the full scenery.

Scenery files are available seperately. You can choose a part of the world to download by viewing a map and clicking on the are you want.

The default base package only comes with the San Francisco Bay area. It may be worth using the bit torrent file to download a larger version if you want more scenery.