The FlightGear flight simulator project is an open-source, multi-platform, cooperative flight simulator development project. The goal of the FlightGear project is to create a sophisticated flight simulator framework for use in research or academic environments, for the development and pursuit of other interesting flight simulation ideas, and as an end-user application. We are developing a sophisticated, open simulation framework that can be expanded and improved upon by anyone interested in contributing.
Flight Gear is a fairly typical OpenGL application in terms of it's performance and hardware requirements. It requires a reasonable hardware accelerated 3D card with OpenGL drivers to achieve smooth frame rates. Software only rendering typically yields frame rates in the neighborhood of several seconds per frame. But, with a 3d accelerated card you can expect much higher. On a 2-3Ghz class CPU with a GeForce card, frame rates in excess of 60 fps are reasonable to expect in most situations. The actual frame rate varies of course with scene complexity (which changes from area to area and changes as your view direction changes) and the specific details of your hardware.