Tom’s Spaceship Miniatures / Games List offers a nice resource for people getting into this type of gaming. FWIW, Silent Death is one of my all time favorite games.
Science Fiction
Installation 42 Print-And-Play
Installation 42 is a free print-and-play deck building game with a science fiction theme. Looks good.
Pocket Imperium Free Card Game
Pocket Imperium is a free card game of the Expand, Explore, Exploit and Exterminate genre. It’s designed for three players (not many of these) and uses just 18! cards.