it compatible with other operating systems. They have received substantial notable coverage. There are hundreds of source ports known to have existed. The Doom engine's source code was released to the public on December 23, 1997. Although Doom was originally created for DOS, the original source release was for the subsequent Linux version, due to the use of a proprietary sound library in the DOS version. The original purpose of source ports was cross-platform compatibility, but shortly after the release of the Doom source code, programmers were correcting old, unaddressed Doom bugs and deficiencies in their own source ports, and later on introducing their own modifications to enhance game features and alter gameplay. The source code was originally released under a proprietary license that prohibited commercial use and did not require programmers to provide the source code for the modifications they released in executable form, but it was later re-released on October 3, 1999, under the GPL-2.0-or-later license after requests from the community. The following diagram depicts a simplified family tree of Doom source ports (note: information may be outdated). Personal computers DOSDoom and derivatives DOSDoom is the first Doom source port for DOS, launched within a day after the release of the Linux game's source code in 1997. It was created by Chi Hoang, who took the original Linux release of the Doom source code and ported it back to DOS. It evolved to include several new features, which were previously unseen at the time shortly after the release of the original Doom source code, including translucency, high resolution and color rendering, and vertical aiming. Doom Legacy Doom Legacy is a source port originally written as a fork of DOSDoom, introducing mouse-look, jumping, a console, 32-player deathmatch, skins, and, later, native Windows, Linux, and Mac OS X ports. It has also evolved to support many Boom features and 3D acceleration. Later releases include additional features, notably the ability for levels to contain floors directly over floors in December 2000, meaning levels are not required to be strictly 2D from a top-down perspective as they were in the original Doom engine games. It has its own scripting language, called Fragglescript. GLDoom One of the first source ports, glDoom was an attempt to bring OpenGL accelerated graphics support to the Doom engine, developed by Bruce Lewis. The project was canceled in 1999 after an accident in Lewis's home, in which the