Meanwhile, Tengen secretly worked to bypass Nintendo's lock-out chip called 10NES that prevented unlicensed NES games from running.

While numerous manufacturers managed to override this chip by zapping it with a voltage spike, Tengen engineers feared this could potentially damage NES consoles and expose them to unnecessary liability, and so they started development on a chip they called Rabbit.

[6][7][8][9] Tengen faced another court challenge with Nintendo in 1989 in copyright controversy over the two companies' NES versions of Tetris.

Tengen lost this suit as well, and was forced to recall what was estimated to be hundreds and thousands of unsold cartridges of its version of Tetris (having sold only about 50,000 copies).

It was best known for its ports of popular Atari arcade games, including Klax, Hard Drivin', STUN Runner, and Paperboy, although they published many other titles as well.

The company's first game was Zed and Zee, an 8-bit arcade-style action platformer for NES, Famicom, and Windows.