Do you like flight simulators? If so, you'll love FlightGear. It is an open-source flight simulator. This means that as long as you abide by the terms of the license you may freely download and copy FlightGear.
Even though this is a free flight sim program, don't think for a moment that it's not worth the price. :) It shows a professional polish and attention to details like wind effects and real-time day and night. That's no surprise when programmers around the world can contribute to the project.
The game includes real-world scenery taken from photographs. The game comes with The San Francisco area built in, but you can visit the FlightGear Web site to get additional settings from around the world, including thousands of real airports.
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.
Here is the link to the home page so you can get a better idea of what the program looks like.