FlightGear Flight Simulator: free open-source multiplatform flight sim
Open Source Solid Modeling CAD
Display, convert, and edit raster image and vector image files
Drawing, graphics conversion, software development, administration.
Picture Database Viewer
Concise spatial query and representation system (c-squares)
Library to correct optical lens defects and lens database
Converts between many 3D data formats
3D .NET engine for Windows, Linux, Mac
PHIGS (Programmer's Hierarchical Interactive Graphics System)
Free drawing software for Windows, Mac OS X, and Linux
Pear3DEngine is a modern and modular 3D development framework