These are single player cheats you can enter at the game console:
AMMO: restore ammo
ARMOR: 200% of armor
CHOJIN: immortality
DEPTH: distant fade
FULLMAP: full map
GO (#): get to specified level
INVISIBLE: 2 minutes of invisibility
KILL: kill all monsters
NOMONSTERS : chasm without monsters
REANIMATE: reanimate all monsters
RESPAWN (#): set the monster respawn time in seconds. (0 means no respawn)
REVERSE: reverse right and left sound channels
SHADOWS (#): set the upper limit of shadows
WEAPON: all weapons
These are multiplayer cheats you can enter at the game console:
KICK (#): disconnect player # from multiplayer game
KILLP (#): kill player #
NICK: shows current name
NICK NEWNAME: set your name for multiplayer gaming