Space Intruders I believe is the first machine language game that Charles Forsythe did for the Coco, and the first machine language game that Adventure International did for the Coco as well. It is also one of the rare machine language games that runs on a 4K Coco 1. Looking at old Adventure International catalogs, it looks like Charles may have done a BASIC 4K Space Invaders clone early (around the summer of 1981), and then this machine language one by around October/November 1981 - but it could also be read to just mean that 4K Standard BASIC was required and the latter was just a name change (Computerware already had a Color Invaders that came out in January of 1981). Irregardless, since this game used keyboard controls, it could be played on a stock 4K Coco with just a cassette player... nothing else was required.
The game itself is kind of a Space Invaders and Galaxian hybrid. The player moves back and forth on the bottom and can only have one shot in the air at a time. The formation of red and white aliens move back and forth like Space Invaders (although faster than the arcade version) but they don't fire at you. But one will peel off (changing color to blue and yellow) and dive bomb (ala Galaxian) and will fire upon the player. The player can earn extra ships (I am unsure if this is score based or wave based), and on later waves you will get 2 dive bombing aliens at a time (it may go higher than that the further you progress. The red and white aliens in formation are only worth 1 point; the dive bombing ones are worth 5.
Like Gauntlet by Britt Monk, Space Intruders features good action and surprisingly good sound for a tiny 4K game.
Title: Space Intruders (I believe originally Color Invaders)
Author: Charles Forsythe
Publisher: Adventure International
Released: Either Summer 1981 (if same game as Color Invaders but renamed) or Winter 1981 (if these were two different games) Pretty sure the former.
Requires: Color Computer 1,2,3, 4K RAM, cassette.