We can start a list. The first one I know of is "7 Mages".
On the 7 Mages official website forums, it is said that GOG turned down this game because "it is turn based".

https://store.steampowered.com/app/446590/7_Mages/

That's a terrible excuse for GOG to use, because there are a ton of awesome turn-based games.

To try and compile such a list would be outright folly, it is unknowable without direct confirmation what they have turned down.

Yeah, and GOG offers lot of them
https://www.gog.com/games?search=Turn-based&page=1&sort=title
Looks like a pretended justification.

Here's one speculative thread:

https://www.gog.com/forum/general/vague_signs_that_a_game_might_be_released_here_not_even_unofficial_confirmations

Why not another one with the topic of games that have been turned down? Seems reasonable enough.

https://store.steampowered.com/app/368080/Aurion_Legacy_of_the_KoriOdan/ Devs tried, GOG refused

How about providing such a list :)

Plenty of devs, like the one I linked, have come straight out and stated that GOG rejected their game. It would be a big enough list if you just compile all of those, no speculation needed.

I think GOG has a pretty good idea of what games would sell well in their store, but it would be nice to know if there are any games that are impossible to get due to GOG's DRM-Free policy. That being said, DRM-Free is the only way to go.

The Quest, another favorite of mine, was rejected. After that I didn't feel so bad buying on Steam.

Who knows what bizarre criteria they have.

The only ones that kind of bother me are ones high on the wishlist, like Hatred now at 4,400+ votes. (I'm not saying GOG doesn't necessarily have good reasons.) And Heroine's Quest (435 votes), which I would have liked to see here despite being freeware.

They rejected Speedy Eggbert from my childhood but I can't really blame them, it didn't have many votes at the time. And other low-wishlist graphically-unengaging or unengaging gameplay games. Plus Eggbert/Blupi games are now freeware. http://blupi.org

Oh cool, I get to post these older games gog turned down again!

https://www.gog.com/forum/general/classic_digital_rereleasing_old_infogrames_games_on_steam/post26

https://www.gog.com/forum/general/classic_digital_rereleasing_old_infogrames_games_on_steam/post27

Drakkhen is the exception as it was finally released....after it was included in a cheap bundle elsewhere though:

https://www.gog.com/forum/general/classic_digital_rereleasing_old_infogrames_games_on_steam/post48

Also, some years ago, someone on the forums pointed out that supposedly there was a Facebook from Zojoi that said the MacVenture series was rejected by gog (Maybe you should release these scary games during October gog, *hint* *hint*):

https://store.steampowered.com/sub/59404/

And who can forget Opus Magnum? A game gog users wanted and only finally got here after it took community outcry and gaming sites covering the initial rejection by gog.

https://www.rockpapershotgun.com/2018/02/01/opus-magnum-overcomes-rejection-to-launch-on-gog/

Gog seriously needs to stop over-curating, or they won't be around another 10 years. And because someone will bring it up, no, i'm not asking for Steam like "anything goes" curation that's flooded with asset flip scams and shovelware, I just want gog to stop rejecting what should be obvious good gets.

Speaking of the 10th anniversary, are you guys getting Celeste here or not? Kind of annoying to show it in this 10th anniversary vid, and then not release it or even say if it's coming one way or the other:

https://youtu.be/vEUqr3yYII0?t=3

https://youtu.be/vEUqr3yYII0?t=366

How is the game? I'm thinking about getting it on Android but I could use some thoughts about it