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Tengen video games for the NES
Tengen was a company formed by Atari to handle the software side of the company. At the time Nintendo had a crazy licensing policy where developers had to sign a contract restricting the software developer to only releasing five games per year and that they would only develop games exclusively for the NES for a two year period. A chip called the 10NES was also mandatory in each licensed cartridge. If the chip wasn't present the game wouldn't play.
Tengen tried to negotiate a better licensing deal but Nintendo wouldn't budge. Therefore Tengen developed the Rabbit chip which allowed their unlicensed games to be played on the NES. It was also discovered that Tengen obtained the patents used to make the Rabbit chip illegally.I won't get into the lawsuits that followed but the distinctive Tengen black cartridges were not just for looks.
Anyone who was a kid in the late eighties that had a chance to play Tengen`s Tetris before it was pulled from shelves knows that it was the superior game over the Nintendo version. An interesting part of video game history.