The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++ and also available for .NET languages. It is completely cross-platform, using D3D, OpenGL and its own software renderer, and has all of the state-of-the-art features which can be found in commercial 3d engines. The authors boast a huge active community, and lots of projects in development. You can find enhancements for Irrlicht all over the web, like alternative terrain renderers, portal renderers, exporters, world layers, tutorials, editors, language bindings for java, perl, ruby, basic, python, lua, and so on. And best of all: It's completely free.
Tool Classification:
Functions=
(Engines - Rendering)
Qualifiers=
(Open source) (Free) (DirectX) (OpenGL) (Linux version available) (Mac OS version available) (Engine, 3D)