Cheat Codes
Shareware or Registered:

GABBAGABBAHEY = Cheats enabled!
SCOURGE = WowieZowie Weapons!
MITZI = All Keys!
RACERX = Invulnerability On/Off!
GUILE = Cloak On/Off!
TWILIGHT = Shields Recharged!
FARMERJOE = Warp to Which Level?
ALT-F = Show full map

Registered only:
BIGRED = Super WowieZowie Weapons!
BUGGIN = Turbo Mode
BRUIN = Extra Life
FLASH = Exit Path Illuminated!
AHIMSA = Robot Firing On/Off!

This is a new cheat in Descent v1.4:

Type ASTRAL to toggle Ghosty mode.
From version 1.4:
POBOYS = Blow reactor
PORGYS = Mega-Wowie-Zowie
LUNACY = Robots move fast, fire seldom
PLETCHxxx = Robot painting with texture xxx (001-999)

Undocumented Map features.

The following features are undocumented:

In the map, hold down "S" and move the control around. You can pan the map this way.

If cheat codes are enabled, hit "Alt-F" in the map screen. The entire map will appear.