Magrunner: Dark Pulse, a sort of Lovecraft-meets-Portal mashup of a puzzle-platformer, has gone free on GOG for the next 24 hours. All you need to do to nab the game is to head over to the GOG front page, scroll down until you see a big banner saying: "Download Magrunner for FREE". Click it and BOOM! Free game. It might take a little while to process, and you'll have to make sure that you're signed into your GOG account, but FREE GAME!
You can check out our Magrunner review here.