Invasion is a 2 player only version of Space Invaders, where both players play simultaneously. It is played in a coooperative mode; both players are trying to kill the same waves of aliens, and can't damage each other. But there is competition in as to who gets the highest score, and it becomes a 1 player game once a player has lost all of their lives. The aliens also descend in an 'S' shape, versus a line of aliens at a time. An interesting take on the arcade classic, from a publisher that shut down soon after this was released so as not to compete with their own advertisers.
I am pretty sure that this was written by David Crandall, as it has the same sound effects as some of his other games, and was also published by Creative Computing Software (the software subdivision of Creative Computing magazine) as was another of his games, Orbitroids (later Orbitron).
Title: Orbitron
Author: David Crandall (?)
Publisher: Creative Computing Software
Released: 1982
Requires: Color Computer 1,2,3, 16K RAM, 2 joysticks, tape.
Download INVASION.ZIP. (contains the .DSK image. It also includes ROML, which you can use to load and run it on a disk system since the game itself was set up for cassette)