[Update]: The next giveaway has now arrived with the physics-based sandbox Kerbal Space Program and the stealth-focused Shadow Tactics: Aiko's Choice!
If you're a fan of stealth games, of if you would like to become one, you'll be pleased to hear that Dishonored - Definitive Edition is currently free to grab! All you have to do is head on over to the Epic Games Store, add Dishonored to your account, and you'll be good to go after a bit of a download.
Naturally, there is a time limit you'll want to watch out for. The giveaway will only last until January 5th, so do make sure to snag Dishonored before it goes away! Once you've done that you'll be able to play it whenever you want and for however long you want.
Personally, I would highly recommend it as Dishonored is an absolute treat for anyone that has even a remote interest in stealth-based gameplay. Each area you have to comb through has loads of different paths for you to take, each problem has multiple solutions, and the various abilities you can unlock offer a great deal of customization so you can play through the game multiple times without repeating the same sort of strategy. Combine that with a well realized world and some intriguing characters, and you've got yourself one of the best stealth games released in the past decade!
Have fun checking out Dishonored, and I'll leave you with one of the original gameplay trailers to help set the mood: