FlightGear Flight Simulator: free open-source multiplatform flight sim
Open Source Solid Modeling CAD
CIRT - CUDA Interactive Ray Tracer
Tao3D is a programming language for real-time interactive 3D
Design and Display Happy Cube solutions
PHIGS (Programmer's Hierarchical Interactive Graphics System)
an interactive 3D viewing program
C++ class library for programming interactive 3D graphics with OpenGL