For the full version:

 Press [~] in the game and then type in

 nitro god         - God mode *
 nitro giveall     - All weapons and ammo *
 nitro givemoney   - Get 999,999 cash *
 nitro killall     - Kill all enemies instantly *
 nitro fly         - Fly mode *
 nitro ghost       - No clipping mode *
 nitro refresh     - Refresh health
 nitro changelevel - Skip to next level
 nitro speed x     - Set movement speed [x = 1 (normal) - 10 (fast)]

 * = Can be deactivated with typing the command again

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 For the demo version:

 Press [~] in the game and then type in

 please god     Unvulnerability
 please money   99999 Coins