AudoDesk
AutoCAD

CompuFoil
(airfoil plotting software)

CRRCsim
A free model-airplane flight simulation program. Primarily sailplane oriented (thermal and slope) but has some powered models also.

CSM Aircraft/Heli Flight Simulator
(distributed by Horizon - this link connects to the Horizon Hobby main site - click on CSM, and then click on Simulators)

Dave Brown Products
(Dave Brown flight simulator)

DesignCAD
(manufacturers of ModelCAD software)

Desktop Aeronautics, Inc.
(aerodynamic analysis and design - Panda, LinAir, Sand)

ElectriCalc
(electric power system performance estimation)

FoilSim
(from NASA)

Gloor's F3Score
(F3B/F3J sailplane contest scoring software)

Hanley Innovations
(VisualFoil)

Helmut Lelke's Design Analysis Program
(well, not exactly a company, but it's on our site, does a good job of initial airframe design, and it's free!)

IMSI
(TurboCAD 2D and 3D CAD software)

Knife Edge Software
(these are the developers who wrote the RealFlight simulator - with more information than you'll find on the Tower/RealFlight site...)

MotoCalc
(electric power system performance estimation)

Multiplex CockpitMaster
(power, slope and thermal simulations, with LAN and Internet multi-player capabilities - note - this sim needs DirectX 7a or higher installed with a fairly modern 3D graphics card)

MWD & Associates
(fueled engine analysis software, high performance boating products)

PCSoar
Sailplane Performance Analysis

RcCad
(A nice inexpensive 3D CAD program that is designed to allow easy creation of solid shaded 3D models - viewable in a browser - and in your browser you can "turn them around", upside down, walk around them...)

RealFlight Flight Simulator

TraceFoil

WinFoil
(airfoil plotting software)

XFoil for Windows