The Talos Principle, which is a science-fiction first-person adventure and puzzle game, is currently free on Epic Games. It expires on the 30th December at 16:00 GMT.
Description:
The Talos Principle is a first-person puzzle game in the tradition of philosophical science fiction. Made by Croteam and written by Tom Jubert (FTL, The Swapper) and Jonas Kyratzes (The Sea Will Claim Everything).
Link:
https://www.epicgames.com/store/en-US/product/the-talos-principle/home