Nintendo Entertainment System:

Encouraged by these successes, Nintendo soon turned its attention to the North American market. Nintendo entered into negotiations with Atari to release the Famicom under Atari’s name as the name Nintendo Advanced Video Gaming System. The deal was set to be finalized and signed at the Summer Consumer Electronics Show in June 1983. However, Atari discovered at that show that its competitor Coleco was illegally demonstrating its Coleco Adam computer with Nintendo's Donkey Kong game. This violation of Atari's exclusive license with Nintendo to publish the game for its own computer systems delayed the implementation of Nintendo's game console marketing contract with Atari. Atari's CEO Ray Kassar was fired the next month, so the deal went nowhere, and Nintendo decided to market its system on its own.g[›]

Please answer a question about this article. If the question is unanswerable, say "unanswerable". Which company was illegally demonstrating a Nintendo game?
Coleco