Attack Of The Zolgear

Attack Of The Zolgear (also known as Galaxian^3: Attack of the Zolgear) is a video game implemented as a conversion kit for Namco's "Theater 6" system, which was used for the 1994 arcade version of Galaxian 3 (which was originally a theme park attraction that debuted in 1990). A sequel to the aforementioned (which also had the subtitle of "Project Dragoon"), this six player game (gameplay for 6 at the same time in this huge 17' x 17' theater) never hit it big like its earlier version. This game used two laser disc players simultaneously for the outer space background, while computer generated graphics were overlaid on top.

Source: Wikipedia, "Attack Of The Zolgear", available under the CC-BY-SA License.