Press BACKSPACE during gameplay, then activate the following cheats by entering the corresponding codes:

CHEAT FUNCTION - CHEAT CODE
God mode - chojin
Full ammo - ammo
200 armor - armor
Invisibility for two minutes - invisible
All weapons - weapon
View entire map - fullmap
All keys - keys
Kill all monsters - kill
Toggle horizon distance - depth
All monsters respawn - reanimate
Set respawn time - respawn <seconds>
Reverse left and right sound channels - reverse
Set upper shadow limit - shadows <number>
Level select - go <level number>
Disconnect player in multi-player mode - kick <player number>
Kill player in multi-player mode - killp <player number>
Show current name in multi-player mode - nick
Select new name in multi-player mode - nick <new name>