Thanks for these lists. I wish this useful information would be included on the game store pages. GOG as alwas not delivering the full service. The community has to do it.

The game page for Mortal Kombat is probably not visible for you in Germany:

Mortal Kombat 1+2+3
NOTE: Mortal Kombat 1 + 2 feature only hot-seat multiplayer while Mortal Kombat 3 features multiplayer through a LAN connection.

+1

Thanks, added.

There is also hot-seat mode in Eador: Genesis (as well as in Eador: Master of the Broken World) and in Warhammer Epic: Final Liberation. I'm not sure about internet + LAN option in case of Warhammer 40k: Rites of War, in theory there are both options available, but I can't choose them to test this mode (when I'm clicking for button "next', it's not going on the next "page").

Dungeons II also has online multiplayer not rquirering Galaxy (personally, I couldn't never connect with server properly, don't know why, I've set firewall to give permission to Dungeons II)

Master of Orion 2016

Multiplayer Notice: GOG Galaxy is required to play multiplayer.

Maybe the ripped the multi-player mode out, like they did in Deadlock 1 according to the sub-forum.
Could anyone else try to confirm it?

Did anyone have success?

I added the rest to the list, thank you.

Thanks.
I have a (bad) feeling the list will get longer than the one without Galaxy when we're through even with the current catalogue.

All modes have DRM except hotseat.

DEFCON, if it's the game I'm thinking of, has DRM.

What the problem with Neverwinter Nights?

Serial registration for both?

Last time I tried playing it in LAN mode, it needed one authentic key each for base game and each expansion, I will add it as soon as someone can confirm that this has changed or it does work with GOG's stub serials.

Grim Dawn currently works without Galaxy, was supposedly a bug.

As expected. ;)

For AoW3 at the start of a game each player has to check with Triumph's server that will then authorize them for that play session. "PBEM" would presumably be per turn. Needs Triumph account.

DEFCON, AFAIK at each launch, checks with the dev's server to see if the serial is still valid. If not it switches the game to demo mode. Not that I would own this, but I don't recall if the Linux installer was ever updated with an always offline unlocked version. Account based via serial key.
Are you redefining what LAN mode is? NWN1 multiplayer is direct IP with dedicated servers. Works LAN, Online and, IIRC, even has updated master browser servers. Anyone with a valid copy can play LAN, GOG finally changed to automated serials for this and, AFAIK, the person running the server can set serial check.

LAN = Local Area Network (Offline)

As I've said, the last time I tried setting up a game with two PCs via dedicated server with the same serial number in LAN, it failed and asked for a different serial, I remember it trying to call home for checking the serials as well and not liking that there was no internet connection available. That was about 12 years ago though and I haven't tested it with GOG's version.
Apart from this being DRM anyway, I wonder whether GOG hands out unique serials for the game in the library in the first place, that's why I asked for confirmation of someone who tried setting up a LAN game of it so I can make the entry with according notes.

The Last Blade requires Galaxy for online multiplayer.

Serious Sam TFE/TSE include split-screen mode, LAN and multiplayer online and these without need a client

Thanks, lists have been updated accordingly.