Stargate is an arcade game released in 1981 by Williams Electronics. Created by Eugene Jarvis, it is a sequel to the 1980 game Defender, and was the first of only three productions from Vid Kidz, an independent development house formed by Jarvis and Larry DeMar. This video game has no connection to the subsequent Stargate franchise that began 13 years later.
The game is also known as Defender Stargate and Defender II. The latter name was used in home video game releases, due to legal issues (according to the bonus material for Midway Arcade Treasures, Williams wanted to "make sure they could own the trademark" on the Defender name). The name Defender II has been used on all of its home ports, and game compilation appearances, however there were never any Defender II arcade units. To complicate matters, the Atari 2600 port was originally sold under the Stargate moniker but was renamed to Defender II for a later re-release.
The player flies a small spaceship above a long, mountainous landscape. The land is inhabited by a small number of humanoids. The landscape wraps around, so flying constantly in one direction will eventually bring the player back to their starting point. The players ship can fly through the landscape without being destroyed.
A number of enemy ships fly over the landscape. The player's responsibilities are twofold:
1. Destroy all aliens
2. Protect the humans from being captured
The player is armed with a beam-like weapon which can be fired rapidly in a long horizontal line ahead of the spaceship, and also has a limited supply of smart bombs, which can destroy every enemy on the screen. The player also has a limited supply of "Inviso" cloaking energy, which makes the ship invisible, and able to destroy any ships it comes in contact with.
At the top of the screen is a radar-like scanner, which displays the positions of all aliens and humans on the landscape.
In July 2000, Midway licensed Defender II, along with other Williams Electronics games, to Shockwave for use in an online applet to demonstrate the power of the Shockwave web content platform, entitled Shockwave Arcade Collection. The conversion was created by Digital Eclipse. It is currently freely available to be played within the shockwave web applet.
It also should be noted that the music from Punchout (1987) for the Famicom and Nintendo Entertainment System, borrowed some music and sound effects from the 1983 Famicom version of Stargate (later released as Defender II in 1988 by Hal for the Nintendo Entertainment System). For example, the music played when the game begins is a longer version of the entrance music of the Little Mac's opponents. Also, after completing a stage, during the intermission screen between waves, the music played is the same as the screen after Mac loses a match.
Source: Wikipedia, "Defender II", available under the CC-BY-SA License.