"If you think that flight simulators are a dying breed then you have missed out on the rise of FlightGear, an open source flight simulator started in 1997 that can be regarded as a game or as a research tool.
The latest version 2.4 has just been released and it has some significant improvements. As always what you consider important depends on your interests, but notable is the overhauled weather module which now sounds more like a weather prediction/simulation system. You can set up some initial weather using METAR reports and the system will generate weather based on the state of the atmosphere and the local terrain. This can result in fog, thermals and topographic clouds. Clearly fun if you are flying a glider and taking the weather into account is now an essential part of the experience.
The source code is available for download and binaries are available for Windows, MacOS 10.5-10.7, Linux and more"
"Introduction to FlightGear
FlightGear is an open-source flight simulator. It supports a variety of popular platforms (Windows, Mac, Linux, etc.) and is developed by skilled volunteers from around the world. 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.
A project I've not heard of before... Watching it now though.
I wish I was a C++ dev, as I'd love to grab the source and see about integrating a Kinect SDK based NUI into it... :P
Here's a couple snaps of it;