The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++. It is completely cross-platform, using D3D, OpenGL and its own software renderers.
The Companion platform supports developing mobile applications based on a building block concept. It consists of a framework, basic reusable modules (e.g., GPS positioning, map display) and a library implemented on top of the .NET Compact Framework.