From Quake Wiki
Quake is a registered trademark of id Software. All other trademarks are properties of their respective owners. Shambler, Fiend and other characters may also be property of id software.
The source code of the Quake engine has been released under the free and open-source GPL license. You can find it on GitHub or the id Software FTP server. Lots of forks have been created, you can find some at Engines
Early versions of the QuakeC source files have been released under the GPL: ftp://ftp.idsoftware.com/idstuff/source/q1tools_gpl.tgz
Unfortunately the 1.06 source does not have a GPL notice attached by oversight. Changes have been backported from the QuakeWorld source to the 1.01 GPL source, you can find the resulting code at https://www.gitorious.org/quakec-v1-01-clean/quakec-v1-01-clean/commit/c313e4e881ecc21ac28e9d5ce1872c621788659c
Some discussion leading to this can be found at http://forums.insideqc.com/viewtopic.php?f=2&t=3073
Original models, maps, textures etc are property of id Software and not available under a free license. There exist a few full replacement projects with GPL license.
The Quake palette, though, has been permitted by John Carmack to be freely distributed (citation needed).
A set of compilers tools has been released as GPL.
|Unspecified user added a To-Do; add here links to forums threads about the legal status of the quake stuff..|