It's a free Open Source Game Engine for Microsoft .NET Framework and specialized on Visual3D Game Engine, It was a cross platform game engine for .NET 2.0 and Microsoft XNA.
RealmForge Built on AXIOM 3D rendering engine, Written in C++ language. Built for .NET-based games.
Its a 3D game engine which built using Visual Basic 6 and C++ using Microsoft DirectX API. Since version 6.5, this engine are using directX 9 and shader support, also rewritten using C++. Until latest expansion there are no word to develop it to support DirectX 9 and Microsoft XNA.
OGRE (Object-Oriented Graphics Rendering Engine) its a game engine which support 3D Graphic. it was a flexible game engine for doing 3D rendering, Written in C++ language to make it easier for creating game with 3D Graphics Support.