fsx

[Mar]

http://www.x-plane.com/desktop/meet_x-plane/

"X-Plane is not a game, but an engineering tool that can be used to predict the flying qualities of fixed- and rotary-wing aircraft with incredible accuracy.

Because X-Plane predicts the performance and handling of almost any aircraft, it is a great tool for pilots to keep up their currency in a simulator that flies like the real plane, for engineers to predict how a new airplane will fly, and for aviation enthusiasts to explore the world of aircraft flight dynamics."

More info here:
http://www.x-plane.com/desktop/how-x-plane-works/

I don't know if that system would be a problem for low end CPU's or not.

[SIM]

I have X-Plane 9 and at one time was spending time on it. But, it seems to me that the community for FSX is much larger. there seem to be many more aircraft available, and a lot of those airframes are freeware. Most of the sites, that had aircraft I wanted, were strictly payware for X-Plane. That also goes for add-ons in general.