What are the differences between "X-Plane" vs. "FSX"?

Flight Simulator X, a Microsoft product, and X-Plane, from Laminar Research, are both feature-rich simulators, but they have some key differences. The main difference is that FSX bases how the plane behaves on figures provided by the aircraft manufacturer — figures that may not be available, particularly for some military aircraft, while X-Plane uses a mathematical approach that determines how each individual part of the plane behaves under certain circumstances.

FSX offers more cockpit features, more photo-realistic scenery and live weather, but X-Plane offers more realistic aerodynamics. Typically, the specifications for how a military aircraft behaves are a closely guarded secret, so how the aircraft behaves in the FSX simulator is a modeler's guess. In X-Plane, the designers analyzed each individual part of the plane and calculated specific figures for drag, lift, etc., for each part, resulting in more realistic simulated flight.

X-Plane also includes an engine that players can use to build their own planes from those individual parts. It's so accurate that some aircraft manufacturers use X-Plane in the design process. Another key difference is that, as of September 2014, X-Plane is still undergoing development and receiving upgrades. However, Microsoft's last release of FSX was in October of 2007, and the company has ceased development of the product.