Enter these at the console. To get the console, right-click on sof.exe in your demo directory and choose "Create shortcut" and then right-click on the shortcut you've created and choose "Properties". Add this to the command line:
+set console 1
It should look something like this when finished:
"c:\....\SOF\sof.exe" +set console 1"
Bring up the console by pressing "~":
heretic - God Mode
phantom - Walk Through Walls
ninja - Enemies Don't See You
elbow - Give Weapons 1-5
bigelbow - Give Weapons 6-10
matrix # - Timescale (replace # with 1-10)
gimme X - Spawn Object/Item X
updateinvfinal - Gives More Ammo
killallmonsters - Kills All Enemies