It's GOGs 10th anniversary and to celebrate they will be giving away 1 of 3 games on October 4 (October 5 Australian time). Shadow Warrior 2 for the next 48 hours
Cast your vote for one of SuperHot, Shadow Warrior 2 or Firewatch and claim your free gift for the game with the most votes.
There are also deals to be had as part of the celebrations including several games that are now available as DRM free including Stellaris and Soldier of Fortune series.
Just noticed they have also released some 10th anniversary packs/collections:
10th Anniversary Collection I: The Timeless Essentials - $6.89 AUD ($5 USD)
* Theme Hospital
* Dungeon Keeper 2
* Another World
* System Shock 2
10th Anniversary Collection II: The Art of Aging Gracefully - $13.69 AUD ($10 USD)
* Dragon Age: Origins
* Owlboy
* Homeworld
10th Anniversary Collection III: The Modern Classics - $34.09 AUD ($25 USD)
* Kingdom Come: Deliverance
* Battle Chasers: Nightwar
* Shadows Tactics: Blades of the Shogun
C'mmoonnnn Shadow Warrior 2 baby!