FlightGear Flight Simulator - Fly Free

FlightGear is a truly high-quality flight simulator. It supports a variety of popular platforms (Windows, Mac, Linux, etc.) and is developed by skilled volunteers from around the world.
  
FlightGear is an open-source flight simulator, source code for the entire project is available and licensed under the GNU General Public License.

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.

Official Features List:

• Over 20,000 real world airports included in the full scenery set.
• Accurate runway markings and placement, correct runway and approach lighting.
• Taxiways available for many larger airports
• Sloping runways (runways change elevation like they usually do in real life.)
• Accurate terrain worldwide, based on the most recently released SRTM terrain data.)
• Scenery includes all vmap0 lakes, rivers, roads, railroads, cities, towns, land cover, etc.
• Nice scenery night lighting with ground lighting concentrated in urban areas (based on real maps)
• Download Hundreds of Additional Aircraft!
• Freedom
• Flight Dynamics Models
• Extensive and Accurate World Scenery Data Base
• Accurate and Detailed Sky Model
• Flexible and Open Aircraft Modeling System
• Moderate Hardware Requirement
• Access to Internal Properties
• Networking options
• Multiple Displays

Download:
FlightGear
Aircraft