By "few", I mean that clearly state that since it's DRM free, it's yours to keep.

Of those tens of thousands you say, including a few I posted in this thread, there are some or even many games that likely not even the devs know that can be played without Steam.

Sorry, I misunderstood.

I didn't realise that when you wrote "one of the few games on Steam that lets you keep the game" you meant "one of the few games on Steam that publicly states it lets you keep the game".

It's my experience that what a developer or an online store publicly states means very little.

Okay, we're all updated with the newly-reported games. I haven't gotten to go back to find the ones with Linux versions that are downloaded automatically with the Windows versions yet, though.

What happened to Panzer Paladin? I don't see it on the list anymore.

Tetris Effect: Connected is DRM free if you run it from the TetrisEffect-Win64-Shipping.exe in the Binaries folder, no special tricks needed. Make sure you go into the options menu in the game and set Offline Mode to on, otherwise the game will crash whenever it tries to connect to any servers (you *do not* need to be online the first time to do this).

That's weird, I didn't touch it. Maybe they added Steam DRM, and someone removed it from the list? If you confirm for me that it still works without Steam, I'll add it back.

EDIT: Holy crap, it's listed in the list as "Paper Paladin" now, and I have no idea why. Fixing.

The new version of Quake (more info here) will launch and save without the client, by placing a steam_appid text file with the number 2310 in the game's folder (path is Quake/rerelease).

Note: You might need to launch the game once on Steam before it works. At least for me, it constantly froze while trying to load an episode before doing that.

Tested on Windows 10.

This is good to know! Yeah, it's always a good rule of thumb to launch every game online with Steam at least once; some games require extra files to be created before they work properly without the client.

Below are the extra information I mentioned.

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Games I previously mentioned that come with executable .html files (OS agnostic):

Learn Japanese To Survive! Hiragana Battle (app/438270)
File to run: /HiraganaBattle/www/index.html

Learn Japanese To Survive! Kanji Combat (app/759440)
File to run: /Learn Japanese To Survive! Kanji Combat/www/index.html

WhiteLily 1：丽丽公主 - Mayo's Grace (app/997750; DLC for app/876850 but can be launched as a separated game)
File to run: /Princess Lili/Mayo's Grace/《丽丽公主》初版/www/index.html

冒险村传说（Tales of Legends） (app/578440)
File to run: /Tales of Legends/www/index.html

Girls and Dungeons 2 (+18 game; app/1096750)
File to run: /Girls & Dungeons 2/www/index.html

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Game I mentioned previously that have extra in-game contents that need to be manually applied:

Lovely Heroines (app/1170290)
To apply the +18 DLC (app/1175010), download it and then follow the instructions of the file /Lovely Heroines/Lovely Heroines Patch 18/Instructions.rtf (open with Word/Libreoffice). Just make sure you back up the game files beforehand.

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Games with DRM free ROMs included:

Second Dimension RetroPak Vol. 1 (app/1137930): Has NES ROMs.
Just need rename the .dat files in /Second Dimension RetroPak Vol. 1/bin/dat/ to .nes for them to work normally in other emulators.

Motor Mash (app/1257950): Has a PS1 ROM.
The Windows executable appears to have DRM, but the files GAME.BIN and game.cue from /Motor Mash/res/ can be run in other emulators right off the bat.

Super Hunchback (app/1539070): Already listed in the wiki, but I could only run the ROM directly, and not the Windows executable.

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Games where each executable behaves in a differet way:

Sonic Adventure DX (app/71250): Already listed, but I could only get it running by using the AppLauncher.exe executable.

Midnight Castle Succubus DX (app/1299320): game_s.exe launches the +18 version of the game. game_sfw.exe launches the version of the game with adult contents disabled. Both run right off the bath.

Tower and Sword of Succubus (+18 game; app/1327080): Includes 2 games. Succubus_sword.exe launches The Sword of Succubus. THE_TOWER_OF_SUCCUBUS.exe lauches The Tower of Succubus. Both run right off the bath.

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Games that include DRM free prototypes:

Tamashii (app/1026400): Base game appears to have DRM, but the game also comes with a password protected file "Bonus.rar" that includes some prototype builds which are all DRM free. You need to get the password in-game, so consider this a gameplay spoiler - the password is 586231571

NeuroVoider - Deluxe Upgrade (app/521010; DLC for app/400450): Includes a bunch of DRM free prototypes for Flash Player, Android, Linux, Mac and Windows in the folder /NeuroVoider/Deluxe Bonus/Prototypes and Commentary/

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Games where the build from one OS includes executables from another OS (non-OS agnostic):

Mutiny!! (+18 game; app/669050): Only tested the Linux build, but it includes a Windows executable, which was what I tested. I still need to test the Windows build.

Wonderland Nights: White Rabbit's Diary (Chinese version; app/1408540): Only has a Windows build, but includes a DRM free Linux executable (WhiteRabbitsDiary.sh).

Femboy Bangers (+18 game; app/1567860): Only has a Windows build, but it includes a DRM free Linux executable as well (FemboyBangers.sh).

My Goddess of Love (+18 game; app/989080): Only has a Windows build, but it includes a DRM free Linux executable as well (MGoL.sh).

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Random things to note:

Sougetsu Ninja: Kikyou (+18 game; delisted; app/1091040) may not work in newer Windows versions (that was the reason it got delisted in the first place). It was still working in the Win10 version I was using when I tested it, but if it doesn't work going forward, people will probably have better luck using an older version of Windows (either as main OS or virtual machine) or a compatibility layer such as Wine.

NeuroVoider (app/400450) has the wrong link in the wiki.

I can't currently connect to Bethesda.net to download the mod, but it seems that official add-ons are a no-go for the time being: https://bethesda.net/en/article/53tAlMd4N1Aptp9PvdxWD/quake-release-notes-and-faq

Thanks for catching that! So it looks like it will function similar to the updated Doom ports eventually.

Second Hazardous Course (app/896070):
* Abstract: includes 2 versions, single player works without Steam but I still need to confirm if the online multiplayer is DRM free.
* Long version: nw_classic.exe launches an older build of the game, and nw.exe launches a newer build. Single player works right off the bat, no special setting up required. Multiplayer appears to work without Steam but I asked in the game's forum on Steam if the server is hosted in the player's machine or if it uses an external server, and now I'm waiting for a reply.
* Details of the test: single player in a virtual machine with Windows 10 that never had Steam installed. Multiplayer between this same virtual machine and a computer that never had Steam installed.
* Additional information: getting delisted from Steam soon.

Speedy Girls - Dream Team (app/894900):
* Abstract: requires steam_appid.txt with the game's app ID to run.
* Long version: place/create a steam_appid.txt file with the game's app ID in the same folder as the exe.
* Details of the test: Tested in a Win10 virtual machine that never had Steam installed. Also has a Mac build according to SteamDB, but I don't have a Mac machine to test it.
* Additional information: delisted game.

Update about Second Hazardous Course's multiplayer (response from the dev): Never heard of this Photon, but looks like it's DRM'd, then.

Jelly Wants More (app/893040): Use the steam_appid.txt method

Arietta of Spirits is DRM Free. Confirmed by the dev on Twitter and I tested myself as well. No tricks required.

Windows 7.