Crystal Space

Crystal Space is a framework for developing 3D applications written in C++ by Jorrit Tyberghein and others. The first public release was on August 26, 1997. It is typically used as a game engine but the framework is more general and can be used for any kind of 3D visualization. It is very portable and runs on Microsoft Windows, Linux, UNIX, and Mac OS X. It is also free and open-source software, licensed under the GNU LGPL-2.0-or-later, and was SourceForge.net's Project of the Month for February 2003.
Engine design.
Crystal Space is programmed in object oriented C++. It is very modularly built with a number of more or less independent plugins. The client programs use the plugins, such as the OpenGL 3D renderer, by registering them via Crystal Space's Shared Class Facility (SCF).
Features.
Crystal Space has modules for 2D and 3D graphics, sound, collision detection and physics through ODE and Bullet.
Reception and usage.
The engine was for instance used for the OpenOutcast and "PlaneShift" projects.