Four Gates to Freedom is an interesting game was was shipped on two cassettes.

The first cassette was an action game. Upon reaching its highest level, it gave
you the code required to unlock the adventure game. You can play it as well -
use the Numpad's Ins key to start the game and fire, and Numpad 2/4/6/8 to move.

Or you can cheat:

The code is "ptlsh". It must be entered lowercase.

You will find yourself at a large metal door with a code input panel. 

The code to open the door is:
enter xineohp

The publisher, Phoenix, made it their name... but backwards.

At this point, you may begin playing the game.