About
This is id Software's official GPL-licensed source release for Quake II (version 3.19), built and tested with Visual C++ 6.0; a Linux build is included, though the release notes say it wasn't actually tested before shipping. As with the Quake 1 source release, the original Quake II data files remain separately copyrighted and aren't included.
Getting started
You'll need to separately own the original Quake II data files, since this release only provides the GPL-licensed engine and game source code, not the game's copyrighted assets.
History
id Software credits Robert Duffy for preparing this release, and — as with the Quake 1 source dump — notes it was made available for entertainment and educational purposes, with a separate commercial license possible for anyone unwilling to comply with the GPL.