This is the first official Quake II expansion: The Reckoning (also known as
Xatrix, as developed by Xatrix Entertainment).

You are part of an elite commando force that must infiltrate a hostile alien
cite.  Once inside, you must scour industrial landscapes, crawl through
waterways and air ducts, navigate treacherous canyons teeming with vicious
mutants, stow away on an alien spacecraft, and destroy the enemy's secret
moon base.  This mission pack features:

  - 18 arduous levels to conquer
  - Added weapons
  - New enemies

This port installs the game.so file, but you still need the original data.

WWW: http://www.idsoftware.com/games/quake/quake2-reckoning/