A free (LGPL) and portable 3D engine written in C++. It runs on GNU/Linux, Windows, and MacOS/X and supports many modern 3D features like shaders, volumetric fog, stencil shadows, physics, skeletal animation, 3D sound, ...

CrystalCore is a semi-free (commercial use is forbidden) game based on the Crystalspace3D engine. It is meant as a tutorial and a good demonstration of what Crystal Space can do.