LGPL Cube C++ Yes 3D Windows, Linux, OS X AssaultCube, Cube zlib Prior generation (means it has a successor), 2D grid-based system, optimized for outdoor not indoor maps Cube 2: Sauerbraten C++ CubeScript Yes 3D Windows, Linux, OS X Cube 2: Sauerbraten, Red Eclipse zlib Efficient 6-directional height map based geometry (versus traditional Polygon soup model), hence the name Cube, FPS engine Dagor Engine Yes 3D Windows, PlayStation 4, PlayStation 3, Xbox 360, Linux, OSX List Proprietary Dark Engine C++ No 3D Windows Thief: The Dark Project, System Shock 2, Thief II: The Metal Age Proprietary Advanced AI and sound features (full control of sound propagation).