Tengen was actually trying to
reverse engineer Nintendo's
hardware lockout on the
NES cartridges while they were still "legitimate" licensees. Supposedly, Tengen was very close to actual completion of the reverse engineering in the
lab (which would probably get them in a heap of trouble lately with the
DMCA) when someone had the bright idea of bringing an
antitrust suit again Nintendo. Then, one of the Tengen lawyers figured out how to obtain Nintendo's hardware lockout documents under the
guise of this
litigation. Instant reverse engineering! Tengen immediately began manufacturing their own cartridges that worked just like any of Nintendo's in performing the hardware
handshake. Ever notice that Tengen games work great in an NES, compared to those
Aladdin or
Color Dreams carts with all the switches on the bottom? (those use flaky electrical means of overloading the lockout circuitry)
Of course, once the truth about the documents was discovered, Tengen lost and was effectively out of business. Had that attorney kept his dick out of the mashed potatoes, who knows what would have happened?
Tengen Tetris is probably one of the most famous of all the Tengen games, as it is the one that sold very few copies before Tengen lost the suit, and was forced to stop distribution of the game. Tengen Tetris is actually far superior to Nintendo's version of the game, but unfortunately much harder to find. It's overall rarity is far exaggerrated though (I have several copies), where Tengen titles such as Ms. Pac Man and Pacmania are far more difficult to locate.
Actually, had Tengen kept their nose clean, legally, Nintendo would have simply pressured every one of their retailers not to carry Tengen products or they would risk receiving less NES games to sell, or being cut off altogether, and Tengen would have still withered on the vine and died.