Vivid3D is an open-source 3D engine with powerful 2D UI.
Modern 3D engine and IDE written using C# and C++.
Portable game engine with main focus on point-and-click adventures
Vivid Engine 2 is an open source 3D Engine coded using C# and C++.
C/C++ , PHP, PYTHON, 3D ENGINES, CHROME NATIVE CLIENT
3D .NET engine for Windows, Linux, Mac
XNA based game engine completely written in c#
A cross-platform game framework based on OpenGL and GObject.
An open source skateboard games engine written in C# and .NET.
Open Source Virtual World and MMOG Development Platform
Multi-Language Wrapper Collection for the Irrlicht Engine