There is currently a massive Night Dive Studio Steam Sale with 61 games currently discounted by 50%-80%. This sale will last until Friday, April 29 at 10AM Pacific Time. Night Dive Studios specializes in bringing back older PC games for new generations of players.
Some of the more prominent titles include System Shock, System Shock 2, Turok, I Have No Mouth and I Must Scream, and multiple Tex Murphy adventures.
You can peruse all the games on sale on the Steam page.