Vivid Engine 2 is an open source 3D Engine coded using C# and C++.
.NET wrapper for the Irrlicht Engine
3D .NET engine for Windows, Linux, Mac
A cross-platform game framework based on OpenGL and GObject.
Pear3DEngine is a modern and modular 3D development framework
Minimalist 3D Scenegraph Management Framework
PixelLight is a cross-platform application framework