Press [~] during the game and type in at the console:

 god         - Toggle God Mode
 ExitLevel   - Level Skip
 noclip      - Toggle Spectator Mode
 kfa         - Get All Weapons And Full Ammo
 heal        - Heal
 FragSelf    - Guess What..
 morph       - Apparently this game has remnants of code of Alient vs. Predator 2.
               You will be morphed to a Marine Actor, but you cannot morph back!

 By Gangsta33, Gangsta33@gmx.at