The Doomsday Engine is an enhanced Doom/Heretic/Hexen source port for the Windows, macOS, and Linux platforms. It is based on the source code of id Software's Doom and Raven Software's Heretic and Hexen. The Doomsday Engine and the associated ports of Doom, Heretic and Hexen have been under development since 1999. The first versions were released in late 1999 and early 2000.
The purpose of the project is to create versions of these classic games that retain the feel of the originals but are implemented using modern technologies such as 3D graphics and client/server networking. A lot of emphasis is placed on good-looking graphics.