Thank you for the nice words. It depends on the topic of the thread of course and there's one thing that never changed since all the years I have been on the forums: GOG community is the greatest when it comes to collecting information that will help the community. It is absolutely amazing how much time people spend to add to this or similar lists because they are aware that they are helping others as well. That being said: Thank you all for your contributions. I will add the latest additions to the list shortly.

Edit: I finally updated the list. Apologies for the delay.

KeeperRL joins the club

Helping The Hotties has ingame achievements.

Hardspace: Shipbreaker has in-game achievements, in the form of "stickers" that you can place on your equipment.

Turnip Boy Robs a Bank and rips a bunch of in-game achievements.

Darkest Dungeon® II also has in-game achievements

Thanks for the new additions. List should now be up to date again :)

Hello!
The games have in-game achievements also:
I Was a Teenage Exocolonist
Omurice Next Time
The Symbiant
The Symbiant Demo
The Symbiant Re:Union
Synthetic Lover
Synthetic Lover Demo

Since that month is over something butt less gay:
Duck Detective: The Secret Salami
Kaptain Brawe: A Brawe New World
Lila's Sky Ark
Three Minutes To Eight

Tails of Iron includes in-game achievements (called Medals)

Thank you, I've added them to the list.

Tiny Breakers Camp has in-game achievements.

Farewell North has in-game achievements.

Spells & Secrets has the same in-game achievements as the demo.

First Cut: Samurai Duel joins the list :)