If anyone can confirm whether Nuclear Throne has daily/weekly challenges, that'd be great.

Were it so easy...

Also, Dying Light has more missing DLC here:

3D Printer Models
Collector's Artbook
Book (Nightmare Row)
Godfather Bundle
Left 4 Dead 2 Weapon Pack

Rune Classic must be updated ASAP, because of the Human Head Studios closure, which means a possible delisting of the game.

The Steam version was updated to 1.11 more than a year ago. This patch contains some important changes, such as improved DirectX 11 and Windows 10 support.

Pretty please, GOG, don't leave us with an outdated game! ):

Regarding "Dracula: Love Kills" (missing Collector's Edition with additional gameplay) I finally received at least an answer from Frogwares. They will checck (I asked if there's any chance to get it on GOG as well since now only Steam users can enjoy it) and reply to me within the next days. Better than no answer ....

Thanks for chasing this up - hopefully it'll be good news.

And a day later here we are, GOG received the latest update for the Linux version of Moonlighter. :)

Also, maybe it's not quite suitable for this topic, but some games have additional versions that are not available in the GOG Galaxy.

For example, Rune Classic contains Rune Gold, Darksiders: Warmastered Edition contains the original Darksiders, every (or almost every) Close Combat sequel has the first Close Combat, and so on. All these additional games are available in the goodies section, but not available for installation and launch directly from the GOG Galaxy.

There are also some games that are combined into one "shortcut" for an unknown reason.

For example, Silent Storm: Sentinels is a standalone add-on, but the GOG version doesn't have a separate library entry for it, while the Steam version does. The same situation with F.E.A.R. and Elven Legacy Collection (this one, by the way, still doesn't have Russian localization, while on Steam it's already available for several years). I believe that I'm not the only person who wants to be able to install and play these games / add-ons separately.

Added:
Train Valley 2 No Custom levels
Grandia 2 No remaster update
Craft the World Grottoes dlc missing

Edit:
Dying Light - Now missing 8 DLCs instead of 1.

https://www.gog.com/forum/general/release_train_valley_2_passenger_flow_c328d/post23

I'd already linked that as a source in the list. ;)
Thank you though.

The Mac/Linux versions of Enter the Gungeon finally got the latest update.

Today I have emailed Defiant Development regarding the outdated Linux version of Hand of Fate 2. They're usually a friendly bunch and reply fairly quickly to my emails. As usual, I'll keep you posted with any responses.

Unrelated, finally managed to get Galaxy of Pen and Paper to add +1 to the title like on Steam. Asked GOG ages ago nothing happened. Asking the publisher myself helped.

I am not sure if it has been mentioned before, but Caravan has cloud saves and achievements on Steam but not on GOG. This is keeping me from rebuying the game here even for 1 euro for now.

Don't know about missing cloud saves but for missing achievements you should post here.

thanks, it's already listed in there

Abandon all hope ye who hoped for Dracula: Love Kills Deluxe content on GOG ... just got reply from Frogwares

"Hey, sorry for such a late reply. I don't think we have any plans to bring the deluxe edition to GOG. Is buying it on Steam not an option for you?"

Well ... maybe my pretty lengthy reply below will make them change their mind - but I doubt it:

"Thank you for the reply. I already bought it on GOG since I dislike Steam .. so no, Steam never was an option. Let me please add that I think it is a shame to treat customers of different stores different without any reason (and I don't see any reason why you should exclude the deluxe content from Dracula on GOG). Both pay the same money (which you have no problems to take) but those on Steam simply get more for their money than those on GOG. Do you think that's fair? Probably not your decision anyway but maybe you could forward my thoughts. I bought all Sherlock Holmes Games on GOG and Magrunner ... but unfortunately I will never be able to experience the additional gameplay from Dracula just because I prefer buying on GOG and supporting them and you there ... that's a sad thing."