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.
Rogue (video game)
Rogue (also known as Rogue: Exploring the Dungeons of Doom) is a dungeon crawling video game by Michael Toy and Glenn Wichman and later contributions by Ken Arnold. "Rogue" was originally developed around 1980 for Unix-based mainframe systems as a freely-distributed executable (public domain software). It was later included in the official Berkeley Software Distribution 4.2 operating system (4.2BSD). Commercial ports of the game for a range of personal computers were made by Toy, Wichman, and Jon Lane under the company A.I. Design and financially supported by the Epyx software publishers. Additional ports to modern systems have been made since by other parties using the game's now-open source code.