The shareware version includes the entire first episode of the game, Marooned on Mars.
NOTE: This game can be played directly in Windows using a third-party engine recreation (see the links section below).
God mode: Press the following keys at the same time: G-O-D. Pressing all three of these will put you in God mode, and will also give you a jump cheat, meaning that when you press the "jump" key, you can fly.
Full items: Press the following keys at the same time: C-T-[Space]. Gives you the pogostick, all the keycards, and full ammo.
Pass through levels: Hold the following keys: [Shift]-[Tab]. Allows you to walk through locations on the map without beating them.
Description by VGTips