Hold down [F1] while playing the game and type

Mukor   God Mode (or start game with windie.exe -god)
Dedly   Weapon that kicks ass
Golrg   Giant
Btiny   Dwarf
Qsave   Quick save
Pause   Pause game
Frame   Screenshot
Tough   Increase skill level
Mecam   1st-person view
Gocam   Fixed camera view
Spcam   Enemy view
Bamff   End level
Gamma   Change gamma level
Sepku   Suicide
Bills   Demo
Ifall   Fall to earth
Hicup   Fly through the air
Silly   Decrease enemy AI
Lunar   Moon gravity
Funky   Changes keyboard layout
Catch   No-Clipping-Mode
Aiaim   Changes AI
Agrav   Changes gravity
Bzone   View changes
Fpers   Sound debug
Goura   Gouraud Shading ON/OFF
Ntrud   Choose an enemy
Plane   Shows points
Nfade   Color fading ON/OFF
Gmode   Faster
Colid   Shows possible collision points