All keys listed here must be used together with the DEL key:

"0" - Weapon status
"1" - Show path to exit
"y" - Destroy reactor
"p" - Paralyze robots
"k" - Shield to 1
SHIFT+"K" - Suicide
"x" - Extra life
"h" - Cloaking device
"r" - Robots stop firing
"'" - Switch viewer (switches to view from another object)
SHIFT+"'" - Switch back to player
"o" - Outline mode (practically useless)
"l" - Lighting calculation on/off (slightly faster)
SHIFT+"L" - Turn on headlight (player becomes light source)
"[" - Sound test
"]" - Next sound
"c" - Cheat menu (very interesting)
SHIFT+"A" - Light powerup (+10 shields and energy)
"A" - Full powerup (shields and energy to 200, all weapons)
"f" - Show framerate
"," - Zoom in
"." - Zoom out
"F8" - Speed test (x1)
"F9" - Speed test (x10)
Speed test means the player is moved into every cube of the level once while measuring the framerate.

First activate cheat mode with "GABBAGABBAHEY", then type one of these cheats:

SCOURGE - WowieZowie weapons (all weapons/100% ammo)
MITZIALL or MITZIA11 - All keys
MITYI - All maps
RACERX - Invulnerability ON/OFF
GUILE - Invisibility ON/OFF
TWILIGHT - Recharge shields
FARMERJOEx - Jump to level x (x = number of your choice)
ALT-F - Complete automap
BIGRED - Super WowieZowie weapons
BUGGIN - Turbo mode
BRUIN - Extra life
FLASH - Path to exit is illuminated
AHIMSA - Robots defenseless / Robot fire ON/OFF
PORGYS - MegaWowieZowie weapons
ASTRAL - Ghost mode (fly through closed doors)
LUNACY - Robots move fast but rarely shoot
PLETCHxxx - Robot outfit with texture xxx (001-999)
COURGE - All weapons, 100% ammo
BIOPSYTOYS or POBOYS - Destroys the reactor immediately