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.
a 3D engine: a library of subroutines for 3D rendering and game development. The library is C++ with a set of Python bindings. Game development with Panda3D usually consists of writing a Python program that controls the the Panda3D library.