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.