About
This is id Software's original DOOM source code, released for non-profit use by John Carmack in December 1997 (cleaned up for release by Bernd Kreimeier); real DOOM game data is still required to use it. As released, the code only compiled and ran on Linux -- the DOS version couldn't be released due to a copyrighted sound library, and the fate of the original Windows port was unknown to the author -- though the code was described as portable to other platforms with effort. It's licensed under the GNU GPL v2, with the underlying IP owned by ZeniMax Media. As sold today (e.g. via Steam), it's an action first-person shooter in which survivors of a demonic invasion of the UAC's Mars research facility fight their way through hell using weapons including a pistol, chainsaw, and grenades.
Getting started
This repository is source code only -- to actually play, you need real DOOM game data, and as originally released the code only compiled and ran on Linux. The finished game is also sold as a commercial release (e.g. via Steam), where it supports both single-player and multiplayer with Steam Cloud saves and Family Sharing.
History
In his included December 1997 release notes, Carmack reflects on the original engine design in retrospect, noting that the core BSP-based rendering approach (horizontal/vertical lines of constant Z with fixed light shading) was fundamentally sound but could be restructured into a single front-to-back BSP walk, and calling the movement/line-of-sight collision code one of the bigger weak points of the implementation. He suggested project ideas for the community, including porting to new platforms, adding rendering features like transparency and slopes, adding gameplay features, and building a 3D-accelerated renderer.