Today's free game on Epic Games Store is a relatively new game that only released earlier this year - Loop Hero. Developed by Four Quarters, it is an endless RPG that takes place after the world ended.
"The Lich has thrown the world into a timeless loop and plunged its inhabitants into never ending chaos. Wield an expanding deck of mystical cards to place enemies, buildings, and terrain along each unique expedition loop for the brave hero. Recover and equip powerful loot for each class of hero for their battles and expand the survivors' camp to reinforce each adventure through the loop. Unlock new classes, new cards, and devious guardians on your quest to shatter the endless cycle of despair," the game description reads.
All you have to do is choose and place your cards strategically through a randomly generated loop. Different cards will bring different benefits and threats to lead you to the final boss.
Loop Hero can be grabbed here.