An excellent Space Invaders clone for the Intellivision system. Supposedly it was legal to clone the game since it was not properly covered under trademarks according to Mattel lawyers (only the name was trademarked).

It was released for the system by Mattel, and was programmed by APh Technical consulting (who did many of the Intellivsion games). It had many levels of difficulty, that culminated in very fast invisible enemies, that you could only tell by their shots down at you. Very interesting. It was a great game, that ate many of my childhood hours (though none as much as Shark! Shark! or Buzz Bombers) I had not had any exposure to Space Invaders, outside of Space Armada, so when I first saw it, I triumphantly claimed that the intellivision game was terrible ripped off. However, I came to learn that the converse was true.

It has made it over to the PC, Mac, and Playstation via the magic of emulation on the Intellivision Lives! compilation.

Edited from http://www.makingit.com/intellivision