kicad 3D is aimed to add 3D realistic feature on kicad pcb CAD
A raytracing framework for optical/non-optical physics simulations
a java based software to convert 2D to 3D images.
https://github.com/horde3d/Horde3D
PNNL Waterfall Visualization Tool
Game engine supporting many 3D/2D formats and graphic effects
Obsolete: use https://github.com/VMML/vmmlib
1st 3D game engine built in C# for .NET, Visual3D Engine's predecessor