Base 666 is a Spear of Destiny mod by Joe Monaghan released very early in 2006. Offers 21 levels, although they are exclusively modified or intact originals from Wolfenstein 3D or (mostly) Spear. New graphics and sounds come predominantly from Blake Stone games. The storyline concerns slipgates and monsters invading from another dimension; you are told to clear the attacked base (nicknamed Base 666) then take the fight to the enemy.
As listed in the readme file: