It appears the Songs For A Hero - A Lendo do Herói (app ID 389170) is DRM free and Final Fantasy VII (app ID 39140), The Deed (app ID 420740), Touhou Luna Nights (app ID 851100) and Rabi-Ribi (app ID 400910) aren't DRM free.
I closed all the Steam processes through the task manager, deleted all .exe files in Steam's installation folder and then tried to open each game (not sure if that's the ideal process, as I have never tried it before).
Songs For A Hero opened straight away.
Meanwhile, all the other games didn't open even after testing a few methods from the wiki.

EDIT: I got the chance to test the games on another PC, and then Songs For A Hero required a file steam_appid.txt with 389170 in it in the same folder as its executable to run.

Another game that seems to be DRM free is Starbound's beta build Enraged Koala. This one can be downloaded directly through Steam, but it requires commands of the Steam console to be downloaded (and the command will only work if you own the game on Steam).

Some more games I tested:

Atari Vault's (app ID 400020) launcher: Gets stuck in a black screen after the game's logo appear. I'll try testing with it again some other time. The ROMs provided by Atari in the installation folder are all DRM free.

Blood Branched Sakura (app ID 1237270): seems totally DRM free, as it opened normally.

Deadpool (app ID 224060; no longer purchaseable): Doesn't seem to get past the initial loading, but it loads fine through Steam.

Final Fantasy X & X-2 HD Remaster (app ID 359870): seems totally DRM free, as it opened normally.

Freedom Planet (app ID 248310): seems totally DRM free, as it opened normally.

Kaze and the Wild Masks's (app ID 829280) last beta before releasing (yes, I forgot to delete it when the beta keys expired): seems totally DRM free, as it opened normally. But it seems to crash if you stay too long in the start screen.

LiEat (app ID 373770): Only the compilation's launcher opens without Steam. The games themselves seem to require Steam.

Little Witch Academia - Chamber of Time (app ID 710470): Seems to get stuck in the initial loading screen if opened without Steam being installed.

Minecraft Story Mode (app ID 376870): Doesn't open. No errors.

A Summer's End -- Hong Kong 1986 runs without steam

I can vouch for this. PCGW states that an update was made to mandate the Steam client, but that's not entirely true - Square introduced an update last year that accidentally broke offline mode, and they reverted back to the old build a few days later. The game's current build is from February 2017 (according to SteamDB) and I can run it without Steam just fine.

I also can vouch for FF X & X-2 being drm-free. However, I strongly suggest the use of the "Untitled" Project X and FINAL FANTASY X/X-2 LAUNCHER+ if you are going to use a controller. Without the first mod, you can't even exit the game without using the keyboard.

When was FFX/X-2 Remaster removed from the list? It used to be on there. Also FF12 doesn't launch my Steam. Just use the appid.txt

Found a new game that runs without the Steam client:

Arx Fatalis

Verified the latest versions of several games that were already on the list:

Baldur's Gate: Enhanced Edition
Delver
Driftmoon: Enchanted Edition
FTL: Faster Than Light
Starbound
Stardew Valley
Stronghold HD
Windward

Game that doesn't work anymore:

Hero Siege

In fact the game seems to be completely broken as it doesn't start at all no matter what I do. Renaming or deleting steam.exe or steam_api.dll inside the game folder doesn't make any difference. Anyone who can confirm this?

All games tested on Windows 10 64-bit.

Anyone here have Sunset Overdrive on Steam and can check to see if it's laced w/ any DRM?

Is Sunset Overdrive on Steam protected by CEG?
(i.e. does it force a Steam client-app boot when running EXE from game-folder direction...or not?).

Is this game protected by any other extra DRM junk (i.e. Securom, Denuvo)?
Does this require any client-app stuff like the newer Xbox for PC App or not?

I see Sunset Overdrive for Windows 10 version on W10 is $5 and Microsoft often allows for up to 10 PC's at once to use their games from their store, so...figured it's worth asking.

No Denuvo and will run fine in offline mode on Steam but still requires Steam to run. It also has some issues with anti-virus programs and needs to be added to your exemptions list.

Thanks for the info. Much appreciated.

Timespinner works without Steam's presence on Windows. If Steam is present to boot like normally it will make the API call to turn it on but if you rename tje executable it will work without. Alternatively, use the steam_appid.txt trick, "368620", this will bypass that action without needing to uninstall or alter Steam's presence.

This is interesting to me, as after that whole update mess happened and Square Enix reverted it to play offline again, I *couldn't* get it to run without the client anymore. But if we have multiple confirmations to the contrary, I'll make sure it gets added back to the list.

EDIT: Unless I'm doing something wrong, it still doesn't fully work without Steam if you have the latest version. Weirdly, FFX-2 works, but FFX crashes after it tells you about autosaving, and the -Will- episode doesn't launch at all. With Steam running, they all work, and the launch-day version that I have backed up works without Steam, but a fresh download still doesn't work outside of FFX-2.

Very strange. I'm not sure what could be causing this; I'm testing all games in the collection on a computer that has never had Steam installed, copy-pasted from another one that does. I'm using the build with ID 753362 according to SteamDB, verified integrity and everything. I have yet to sit down and play these games in-depth but I can enter the menus and introductory cutscenes without trouble.

I'm a moron, it works. I had something taking control of my GPU, so it wasn't letting the games launch. I just got them to work. I'll add them again when I update the wiki.