A castle full of cats - Arcade mode, that unlocks after completing the game, requires both Galaxy and being online.

Age of Wonders III - cosmetic/name only: it is impossible to create a single player profile. Without connection to the server you have to play as 'Guest'.

Baldur's Gate 3 - has Twitch drops which require Galaxy and a connected Larian account. And Twitch of course.

Battletech - cosmetic. Decorations and emblems, that disappear from single-player if one isn't online.

Beat Hazard 2 - online DRM. The game can't be started at all without being online. It is fully DRM-ed!

Carcassonne Tiles & Tactics - the 'free' DLC "The Abbot" requires a third party account and registration with the publisher.

Coromon - contains a cosmetics shop that is only available if you are online (Galaxy and CoroNet dependency)

Cyberpunk 2077 - Rewards, which are single-player content, require connecting the game to your account via Galaxy. A blue one officially stated this.
Cyberpunk 2077 - Piggyback Interactive Map - requires an online connection to a 3rd party to work.
Cyberpunk Phantom Liberty- contains cosmetic content and special weapons that are locked behind a required connection of your account to Twitch and watching Twitch streams.

Disciples II - Rise of the Elves - added a mini-campaign in v3.01, which requires Galaxy.

Dragon's Dogma: Dark Arisen The strongest armor set in the game (which is usable in single player) and some masks can only be obtained by fighting the online Ur-Dragon. The offline version never drops them.

Dying Light - 'free' weapons and other items that are only available in Singleplayer if you go online.

Expeditions: Rome - has Twitch drops. I.e. DRMed content distributed through Twitch. Strictly speaking this DRMed content isn't sold by GOG but added via someone else, but it is enabled by GOG, through Galaxy. So YMMV whether this counts as DRM in a GOG game or is 'just second class treatment'.

F.E.A.R. - arguably a bug that stays unfixed. Securom remnants weren't removed and can cause the single player game not to start. See post 41

Forced Showdown - contains a warning: you need to be online via Galaxy to access some features. However, those don't even work. So that content would be DRMed by design, but is in reality just not available. See here.

King of Seas - Possibly a bug, but it isn't possible to save the game without Galaxy.

No Man's Sky - the quicksilver shop required you to register online. However, that requirement was patched out by Hello Games in v3.13.
But as of version 3.84_Sentinel_84011, the offline version is again missing features: pure offline players recieve no discovery rewards from The Anomaly, no free emergency broadcast missions and no Quickilver missions from The Nexus. Discussed here: https://www.gog.com/forum/general/drm_on_gog_list_of_singleplayer_games_with_drm/post745

Prison Tycoon: Under New Management - the main game is DRM free. The add-ons require Galaxy. They don't show up in game after an offline installation on an offline computer.

Saintsrow - The Third Remastered - character designs are only stored through Galaxy. As are keybindings and some other settings. Update June 2022: GOG stated a year ago that they would investigate the issue. But it wasn't fixed.

Spellforce 3 - Skirmishes against the AI require an online connection.

Stronghold: Warlords - cosmetic. Some Warlord-skins are locked behind an online registration.

Synthetik: Legion Rising - some weapons and other starting gear are locked behind a Galaxy requirement and a newsletter registration.

Tales of Maj'Eyal - While the game itself is GPL-ed open source, an online connection (and account with te4.org) is required to gain access to extra features like in-game special events and cosmetic addons. Details here.

The Last Blade 2 - supposed offline achievements only: the 'game progress' Gallery is only saved via Galaxy. There are separate online Galaxy achievements. The gallery is something different. The game doesn't have save games, being an old arcade game. Instead, it saves progress in the form of gallery pictures. But those unlocks are only saved online.

The Witcher 3 - Wild Hunt - the rewards introduced in the update in 12/2022 require Galaxy. GOG pretends that they are 'rewards for owning the game' but they aren't available in the offline backup installers. You have to verify your game by starting it through Galaxy. https://www.thewitcher.com/en/my-rewards

Two Point Hospital - part of the single-player content is gated through online connectivity. I.e. one has to register online and be online to unlock. Plus: core gamplay mechanics (staff handling, diagnostics) are bugged in offline mode.

Warhammer Underworlds – Shadespire Edition - needs an online connection for cosmetic content and to stop nagging. See here and here for details.

X4 - Foundations - cosmetic. Online registration is needed for some ship designs, paints and features.

Battlefleet Gothic: Armada 2.: Not DRM, but the game installed EAC. Which can be disabled with the -noEAC option. Check reviews.

Screencheat doesn't even start without Galaxy.

Streaming is the literal plague of DRM Free, most anti consumer practice in the industry. No thank, if i wanted to Stream games i would have bought the games i own here on my steam account. The whole purpose of people buying from gog is to have a consumer friendly alternative to Steam, plain and simple.
Crysis Warhead 32 bit version, build "1.1.1.711 (gog-4)" - still had the 'chicken' DRM active. But it was removed from GOG 'for technical reasons'. Now only the 64- bit version is available.

Cult of the Lamb - game froze during the first sermon, rendering further progress impossible, unless one plays the game through Galaxy and is online. The game was therefore fully DRMed, but that was fixed in the Relics of the old Faith update, Apr.2023

Fishing: North Atlantic - Scallops Expansion. - does not work without Galaxy. In other words: this DLC is COMPLETELY DRM-ED!
DRM was removed by a patch in 01/2024

HITMAN - Game of The Year Edition - ALL the progression (completed challanges, unlocks like weapons, disguises, gadgets and starting points) is only stored online. Also, like the game page admits, some single-player missions (escalation, elusive target) and user created content require an always online connection. But the game was removed from GOG, following protests from the community.

Hybrid Wars - one of three characters for single-player was only available through online registration. The game was removed from GOG. Of course the game is still available for those that bought it. But at least it isn't sold any longer.

Nex Machina required Galaxy to save your highscore, which unlocks further levels. That meant those levels stayed locked if you didn't use Galaxy! But it was fixed. Don't know when the fix occurred, but as of March 2021 it is DRM-free for single player again.

Necrobarista - not DRM, but it was a bug: Neverending loading screen between episodes, that only goes away if Galaxy is running. But it was fixed with the October 2021 patch. The lead programmer took care of it personally.

Northgard - solo mode required Galaxy. But according to GOG and the devs, that was a bug and as of 02.04.2021 the solo mode is DRM-free again. ... However, it was still not possible to select opponents for skirmishes in offline mode. You need to be online to select an opponent for offline skirmish mode. But as of 05.06.2022 solo mode now doesn't require Galaxy to select opponents anymore. Northgard is finally DRM-free again.

Sniper Ghost Warrior Contracts - had spyware (arguably not DRM. You decide.): "Easy Anti Cheat" spyware was installed with the game, which is especially ridiculous, since the game doesn't even have multiplayer, according to it's page. However, it was removed in patch 1.08 (https://www.gog.com/forum/sniper_ghost_warrior_series/sniper_ghost_warrior_contracts_changelog/post4)

Starsand - Depended on Galaxy, but this was fixed.

Sudocats - the 'Random Puzzle' game mode required Galaxy. Without Galaxy, the game crashed. Seems to have been a bug that was fixed.

Tempest - crashed when started without Galaxy. Fixed in update 1.7.5

Wasteland 3 The pre-order goods required online verification, but that was patched out in patch 1.3
GWENT - microtransactions are the sole reason for this game to exist. So of course it needs DRM, because otherwise the purchases couldn't be related to an account. A micro-transaction driven game on GOG was quite a shock at the time. By now almost everyone has gotten used to it and the game set a precedent.

Dishonorable mention: Thronebreaker While neither a multiplayer game nor itself DRM-ed, buying Thronebreaker will also add the above mentioned Gwent to your account, if you want or not. Also it adds some DRM-ed bonus content to Gwent.

List of games that require GOG Galaxy for multiplayer, if there is more (like a third party account), it will be mentioned in the description. Please note, that GOG will NOT warn on the game page about the Galaxy requirement in all cases. Sometimes they 'forget' that warning.
8-Bit-Armies and Hordes
A Game of Thrones: The Board Game - local multiplayer is not supported and online play requires an asmodee.net account
Absolver
Age of Wonders 3: All modes except Hotseat require a unique CD key, which will be located in your game shelf, and an on-line account with Triumph Studios.
Alien Versus Predator Classic 2000
Ancestors Legacy
Aragami
Ashes of the Singularity
Baseball Stars 2
Battletech: third party. you do need a Paradox Account to challenge other players in 1v1 multiplayer matches and to redeem unlock codes for Kickstarter Backer or Pre-Order DLC.
Battlezone 98 Redux:
Carcassonne - Tiles & Tactics: third party account required for online multiplayer.
Craft The World + DLCs
Deathtrap
Descent Underground
Double Dragon Trilogy
Dragon's Dogma: Dark Arisen
Dying Light
Garou: Mark of the Wolves
Gauntlet™ Slayer Edition
Gauntlet™ Slayer Edition - Lilith the Necromancer Pack
Gremlins Inc.
Homeworld® Remastered Collection
Homeworld: Deserts of Kharak
Iron Harvest
Master of Orion 2016
Metal Slug, 2, X and 3
NecroLand: Undead Corps - online battle royale...
No Man's Sky:
Northgard
Offworld Trading Company
Phantom Doctrine
Rise of the Triad (2013)
Roboquest
Serious Sam's Bogus Detour
Shadow Warrior 2
Shock Troopers
Shock Troopers: 2nd. Squad
STAR WARS™ Battlefront™ II (Classic, 2005) - Also has a Galaxy-free multi-player version (classic installer)
Streets of Rage 4
Stronghold Crusader 2
Synthetic Legion Rising
THE KING OF FIGHTERS XIII GALAXY EDITION
The King of Fighters '98 Ultimate Match Final Edition (unverified)
The Last Blade
Tooth and Tail
Trine 3: The Artifacts of Power
Twinkle Star Sprites
Vikings-Wolves of Midgard
Warhammer 40000 Battlesector (either Galaxy or Slitherine account required for multiplayer)
Wingspan
Witcher Adventure Game, The
Worms W.M.D

This is a bug. A kind person said how to fix it but sadly I have lost the browser tab where they explained what to do so I can't play it yet. Hopefully I'll come across it again one day.
I don't think it was in a thread about the game itself. Might have been in a sale thread so it's difficult to search for :/

Luna.... well as most online services you need a pretty good connection which i honestly don't have, it takes me many hours to just download a purchased game so tbh LUNA with GoG will not benefit my life in any shape or form cause it's based on an online service i can never use due to my connection..I tried to use Luna via Amazon and couldn't due to the connection requirements so I for one already feel neglected and shafted, i prefer having non DRM games even if they can take hours even days for me to download at least i know it's legally mine in the end when i have it.

TBH I would have preferred the "NEWS" of GoG getting some old EA games like Dragons Age 2 or Inquisition etc, or the arrival of Dragon's Dogma 2 since they have 1 or even a NON-DRM version of Diablo 2 Remake or how about a version of Diablo 3 since they released 4 ?

GoG please stick to the non DRM Games and working on having all the "Single" player games from Steam on GoG....
As they say, where there is a will there is a way, make it happen GoG :)

Rename the Galaxy64.dll and the game will still start and save as intended. The Galaxy64.dll however is needed for achievements in Galaxy so if you want those you should not rename it but you will have to play using Galaxy.

No it isn't. Not in this case as you still own the DRM Free copy even if you buy it through Amazon Luna. This 100% idea way to handle streaming. Nothing changes for you at all in the way you buy and receive GOG games. This is complaining about an OPTIONAL feature. If this was Stadia were you had to buy the games and don't get the game files or a subscription service like game pass you would be correct... but this isn't the case.

If I can buy my GOG games and have a DRM free copy on PC and install Amazon Luna on my android tv and phone and steam my owned games... this is a win. It's not something I'd use often but it's nice to have the option.

Question: What about modding? Can't exactly mod on "The Cloud", and I know there's more than a little jank with games like Skyrim 2077.

The vast majority of games you are not going to mod. If it is a game that has modding like Skyrim... then simply mod it on your PC like you do now and play there. This doesn't take away options... only adds to it.

apart from everything else Dragons Dogma 2 has a clear pay to win system.... i'd personally be okey with Gog allowing it but i also have zero interest in owning or playing it

An optional feature which we're pushing back against so it doesn't become the only feature. A feature which at its very core is against the notion of DRM-free. A feature which feeds a trend in gaming which is to the detriment of traditional install-type PC games. A move signalling that GOG is becoming / has become DRM agnostic. A feature which will lead to Support getting more non-GOG related support requests. A feature which gives free advertising to the Amazon platform, and may very well entice GOG users to buy direct from them to use the same service.

It's a slow poison, mate.

Maybe you don't mod, but I do. Compatibility tweaks, accessibility, various source ports, what makes you think I want to play vanilla Caesar III?

Technically it doesn't have p2w. It has pay to skip gameplay, which is the sole reason for the existence of games.

It's a typical capcom bullshit move that they used for over a decade now. I don't expect them to ever release their games on GoG due to this crap and their insistence on using online drms and, recently, anti modding software.

Yes... because the doom and gloom as certainly turned out correct in the past. We all know this isn't gonna replace DRM free or installers but some will complain about it anyway. Maybe you should view it the opposite way, more people via Amazon become aware of GOG and that in turn brings in more GOG users. God knows they could use it and more income.

Or would you rather this place die a slow death mate?

I mod quite a bit. Bust most games don't have large modding communities. That's just a fact. However, then this feature would not be for you.... doesn't mean it's a bad feature to have.

Preach it brother, seems like some people gon't get it when you give a litlle, and little by little you get the boiling frog effect, and all of a sudden you find yourself having the consumer friendly options being gone without people realizing, all in the name of lazyness and convenience ... i just don't get it if people are so into these things why aren;t you people going to Steam or Epic or the streaming platforms directly ? Why do you have this feel to ruin a good thing for the others who want an alternative to anti consumer practices, it's like joining a retro car club and some of you wanting to shittify the old ways be retro fithing with un-important replacement parts, then yelling " IT'S ALL OPTIONAL ", all of a sudden you get this dilluted experience in the name of OPTIONS, if you want modern options go to platforms that use that, stop trying to change what GOG Advertise since DAY 1. I've seen these kind of things happening to companies by the years, companies that started with a slogan and ended up doing the exact same thing they said they wouldn't, google is one of the biggest examples of that, if you remember the " do no evil " slogan. Guess what they did a lot of shady things to customers and there's even a site called killedbygoogle with tech they either invented and killed or companies they bought and killed to remove competition. So excuse us if we aren't buying the OPTIONAL features, think i pretty much demonstrated above that there are games that are broken or unusable without the OPTIONAL gog galaxy client.

Yeah, yeah keep defending anti-consumer corpo practices ... i don't get it how there's always someone white knigthing for a corporation. And for your info gog sales and market share is growing, it's doing better that previous years, and here is you talking about it's slow death xD.