I would like to bring your attention on a web site made by a French developper and flight simulation enthousiast which offers quite a few free interesting programs for advanced flight simulation.
This is what it says:
Welcome to the Flight Simulator Aircraft
Dynamics and Navdata site. You will find here
material and software I designed for Microsoft
Flight Simulator, navaids and fix updates for
FS9/FSX/P3D, aerodynamics links, aircraft
data and airfile design tools and resources as
well as a few other utilities.