Doom (1993 video game)
The ability for others to create custom levels and otherwise modify the game using WAD files turned out to be a popular aspect of "Doom". Gaining the first large mod-making community, "Doom" affected the culture surrounding first-person shooters, and also the industry. Several future professional game designers started their careers making "Doom" WADs as a hobby, among them Tim Willits, who later became the lead designer at id Software.
Doom WAD
Immediately after the initial shareware release of "Doom" on December 10, 1993, enthusiasts began working on various tools to modify the game. On January 26, 1994, Brendon Wyber released the first public domain version of the Doom Editing Utility (DEU) program on the Internet, a program created by "Doom" fans which made it possible to create entirely new levels. DEU continued development until May 21 of the same year. It was made possible by Matt Fell's release of the Unofficial "Doom" specifications. Shortly thereafter, "Doom" enthusiasts became involved with further enhancing DEU. Raphaël Quinet spearheaded the program development efforts and overall project release, while Steve Bareman lead the documentation effort and creation of the DEU Tutorial. More than 30 other people also helped with the effort and their names appear in the README.1ST file included with the program distribution. Yadex, a fork of DEU 5.21 for Unix systems running X, was later released under the GNU/GPL license. (Carmack additionally released the source code for the utilities used to create the game, but these were programmed in Objective-C, for NeXT workstations, and were therefore not directly usable for most people, who were PC users.)