X-Plane is one of the world's most comprehensive, powerful flight simulators, and has the most realistic flight model available for personal computers. It comes with subsonic and supersonic flight dynamics, sporting aircraft from the Bell 206 Jet-Ranger helicopter and Cessna 172 light plane to the supersonic SR-71 and Space Shuttle. X-Plane comes with 35 aircraft spanning the aviation industry (and history), and several thousand more are freely downloadable from the internet.
Full release notes are available here
Note: The download provided here is an installer application you could use to install the app itself