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 software, licensed under GNU Lesser General Public License, and was SourceForge.net’s Project of the Month for February 2003.
It can optionally use OpenGL (on all platforms), SDL (all SDL platforms), X11 (Unix or Linux) and SVGALib (Linux). It can also optionally use assembler routines using NASM and MMX.