Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. Crystal Space currently runs on GNU/Linux, general Unix, Windows, Windows NT, and MacOS/X. It can optionally use OpenGL (on all platforms), SDL (all SDL platforms), X11 (Unix or GNU/Linux) and SVGALIB (GNU/Linux). It can also optionally use assembler routines using NASM and MMX. It supports:

• True six degrees of freedom
• Colored lighting
• Lightmapped and stencil based lighting
• Shader support (CG, vertex programs, fragment programs, ...)
• Mipmapping
• Portals
• Mirrors
• Alpha transparency
• Reflective surfaces
• 3D sprites (frame based or with skeletal animation using cal3d animation library)
• Procedural textures
• Particle systems
• Halos
• Volumetric fog
• Scripting (using Python, Perl, Java, or potentially other languages)
• 16-bit and 32-bit display support
• OpenGL
• Software renderer
• Font support (also with freetype)
• Hierarchical transformations
• Physics plugin based on ODE