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.
DRL (video game)
The game was created by programmer Kornel Kisielewicz with Free Pascal, and uses art by Derek Yu. The developers based DRL in the popular first-person shooters "Doom" and "Doom II" universe.
Since approximately 2002 in-development with first beta versions, the latest stable release is from 2013.