autoaim_horizontal = 1 Autoaim left/right
auto_aim vertical = 1 Autoaim Up/Down
no_camera_boundaries = 0 Camera is not stopped
player+demo_invulnerability = 1 Demi-God mode. Take damage, but not killed
show_fps = 1 Frame rate per second displayed
show_polys = 1 Polygons Per Second Displayed
show_enemy_tactical = 1 See where Enemies will move and attack
debug_console_commands = 1 Show console commands

In game hit "F8" for the console. Before any cheat is typed though you always have to type this first:

externInclude developer:-  So if the cheat code was "God" it was be:

externInclude developer:God  -  Got it? And its Case sensitive too so make sure you get it right! Here are the cheats:

Code Effect

closeallremotedoors Closes all the doors.
disableAllAI Disables AI including enemies and doors.
fullhealth Full health.
givestuff Get all weapons!
giveallkeys Gives you all keys.
hideGUI Hides your HUD!
stuffed Invincible, Full Health, lots of ammo, 9999 Flashlight, 50 Upgrade Parts and all weapons!
setMissionFailureCounter 1 Lose the current mission! (Glitchy if used in demo)
open_door Open a door, good for locked ones.
openallremotedoors Opens all the doors.
quit Quits the game and brings you to your desktop.
disableHostileAI Re-enables them so they can move.
reloadstuff Recieve ammo and full flashlight.
showGUI Shows your HUD!
spawn_alienattack Spawns tons of aliens!
enableHostileAI Stops enemies from moving, but they can attack if you get to close.
loseallkeys Takes away all keys.
enableAllAI Turns AI back on.
warpforward Warp a little ahead on the map.
warpmore Warp ALOT farther on the map.
setMissionSuccessCounter 1 Win the current mission!
immortal You can't die.