Now expired, thanks for the heat everyone :)
GoG.com are giving away Magrunner: Dark Pulse for free for 24 hours only, ends 2pm BST tomorrow (19th). No, you won't get a Steam key, it's DRM-free.
Link is on the front of GoG.com's website. Took about ten minutes for me to get my copy in my account, but I daresay it'll take longer as more people nab it.