Reminder: There's a bunch more on there that expire soon.
https://www.gog.com/connect
AI War: Fleet Command
Amnesia: The Dark Descent
Ascendant
Brutal Legend
Cosmonautica
Darwinia
Deathtrap
DEFCON
Democracy 3
Deponia
Depths of Peril
Downwell
Dropsy
Earth 2140 Trilogy
Earth 2150 Trilogy
Earth 2160
Evoland
Frozen Cortex
Frozen Synapse
Gratuitous Space Battles 2
La-Mulana
Men of War
Metrocide
Not a Hero
Puddle
Redshirt
Reigns
Ren Explorers: International Society
Reus
Shadowgrounds
Shadowgrounds Survivor
Sir, You Are Being Hunted
Stacking
Tharsis
The Last Federation
The Walking Dead: Season 1
Time Gentlemen, Please! + Ben There, Dan That!
Unepic
Vertical Drop Heroes HD
War for the Overworld
X2: The Threat