In 1982, Coleco launches a plug-in for its console, ColecoVision. This device enabled the ColecoVision to be compatible with the Atari 2600. In more simple terms, you could play with the Atari 2600 cartridges on CoelcoVision with the Gemini. You guessed it, Atari sues Coleco for patent violation. However, the court concludes that there is no patent infrigement, since Coleco did not use any Atari 2600 components.
The major difference between the Atari console and the Gemini is the controller design. The Coleco Gemini controller featured an 8-way joystick and a 270-degree paddle on the same controller. The Gemini was also much more compact than the Atari 2600. Also, we must not forget to mention that the Atari console came with the Combat game of 1977, but the Gemini came with Donkey Kong, Carnival or Mouse Trap. These games were much more interesting.