The hacking simulation Hacknet is free for a limited time through the Humble Store. The game normally costs 14.99 euro but for the next 48 hours you can get it for free.
To get the game, just go to the Hacknet: Deluxe page on the Humble Store, and click "Add to cart" then "Checkout". After that click "Get it for free." Once you get the game, it will be yours forever. The offer ends on Saturday, May 26 at 10 a.m. PT. But be careful, because the keys cannot be redeemed after June 9.