A few more I've found:
Crusader Kings II (Just the base game but if you play multiplayer you can use all the host's DLC) gog.com/en/…_ii
Helium Rain gog.com/en/…ain
Heroine's Quest: The herald of Ragnarok gog.com/en/…rok
Nehrim: At Fate's Edge (Requires owning TES: Oblivion on GOG) gog.com/en/…ge
Relic Hunters Zero: Remix gog.com/en/…mix
Wolfenstein: Enemy Territory gog.com/en/…ory (edited)
Crusader Kings II (Just the base game but if you play multiplayer you can use all the host's DLC) gog.com/en/…_ii
Helium Rain gog.com/en/…ain
Heroine's Quest: The herald of Ragnarok gog.com/en/…rok
Nehrim: At Fate's Edge (Requires owning TES: Oblivion on GOG) gog.com/en/…ge
Relic Hunters Zero: Remix gog.com/en/…mix
Wolfenstein: Enemy Territory gog.com/en/…ory (edited)
gog.com/en/…rtx
gog.com/en/…are
gog.com/en/…000
gog.com/en/…ame
gog.com/en/…ght
gog.com/en/…_12