Not only ports, but the actual original source, see Fabien Sanglard's work: https://fabiensanglard.net/ https://fabiensanglard.net/ He has a "[Game Engine] Bla

Not only ports, but the actual original source, see Fabien Sanglard's work: https://fabiensanglard.net/ https://fabiensanglard.net/ He has a "[Game Engine] Black Book" series where he touches old games, its full development history and so on. The Doom one is pretty good.