About
This is id Software's official GPL-licensed source release for Quake (1996), covering WinQuake, GLQuake, QuakeWorld, and GLQuakeWorld, built and tested with Visual C++ 6.0 plus assembly-language routines that can optionally be swapped for a C-only build, at a real performance cost in the software renderer. The original game's data files remain separately copyrighted and aren't included.
Getting started
You'll need to separately own Quake's original data files (or use one of id's old shareware demos, which carry their own redistribution restrictions), since this release only provides the GPL-licensed source code, not the game's copyrighted assets.
History
id Software released this GPL source dump for entertainment and educational purposes, crediting Dave 'Zoid' Kirsh and Robert Duffy for preparing the release, and noted it would consider a separate commercial license for anyone unwilling to comply with the GPL's share-alike terms.