Helix Toolkit is a collection of 3D components for .NET
3D Engine c++
.NET wrapper for the Irrlicht Engine
3D .NET engine for Windows, Linux, Mac
XNA based game engine completely written in c#
https://github.com/horde3d/Horde3D
1st 3D game engine built in C# for .NET, Visual3D Engine's predecessor
A modern 3D App framework using OpenCL to render via raytracing