FlightGear Flight Simulator: free open-source multiplatform flight sim
CIRT - CUDA Interactive Ray Tracer
Rayshade raytracer
Tao3D is a programming language for real-time interactive 3D
Program for drawing 3D surfaces from parametric equations
Gphoton in a simple 3d modeler and ray tracer.
Perl bindings to the Modern OpenGL API
3D .NET engine for Windows, Linux, Mac
realtime 3d surface rendering library
Imagin Raytracer is a multithreaded command line raytracer
3D game engine for C and C++
Pear3DEngine is a modern and modular 3D development framework
Multi-Language Wrapper Collection for the Irrlicht Engine
Bruno's RAY Tracing Engine
C++ class library for programming interactive 3D graphics with OpenGL