The id Software FTP directory offers a little QuakeCon gift from id Software, as it now hosts the public C source code for
Wolfenstein: Enemy Territory,
Return to Castle Wolfenstein single player, and
Return to Castle Wolfenstein multiplayer (all direct links), which are all available under the
GNU General Public License. These source releases contain no game data, so a retail copy of
Return to Castle Wolfenstein will still be required to access assets from that game, while
Wolfenstein: Enemy Territory is free, and still available through
Splash Damage. In each case the game's EULAs are still in full effect. The files are mirrored on
Gamers.org. Thanks Frans.