Space Invader Games

There were plenty of choices for Space Invader-type games on the Spectrum. The two I remember most fondly are Space Raiders and Galactians (easily confused with Galaxians).

Space Raiders had the bunkers at the bottom for you to hide under and shoot a hole through the middle for firing at the invaders but Galactians left you on your own against teams of swooping invaders. Does gaming get any simpler but any more addictive than this? (Actually, it does.)

Download Space Raiders
Download Galactians
Download Galaxians