The Open Toolkit library is a fast, low-level C# wrapper for OpenGL
Vivid3D is an open-source 3D engine with powerful 2D UI.
a 2D Game Development Framework
Vivid Engine 2 is an open source 3D Engine coded using C# and C++.
3D .NET engine for Windows, Linux, Mac
A modern 3D App framework using OpenCL to render via raytracing