The Irrlicht Engine is an open source realtime 3D engine written in C++. It is cross-platform, using D3D, OpenGL and its own software renderers. OpenGL-ES2 and WebGL renderers are also in development. It is a stable library which has been worked on for nearly 2 decades. We've got a huge community and Irrlicht is used by hobbyists and professional companies alike. You can find enhancements for it all over the web, like alternative terrain renderers, portal renderers, exporters, world layers, tutorials, editors, language bindings and so on. And best of all: It's completely free.