Take Brutal Legend for example. The online multiplayer is Steam only. GOG version doesn't "require" Steam, because they are two different stores...I'm not sure if you are pulling my leg or something. Armello had multiplayer for Steam only and was eventually taken off GOG. You might say there are "tons" of them, I don't know what they are and how to find them. I think the multiplayer tag here will give local multiplayer games as a result. Have a nice one.

Welcome; you are a little late for the party, since GOG is becoming Steam soon or worse than Steam, Epic Games Store or even worse than that One Abomination of all or almost all game launchers/clients!

Greetings! I hope that you will enjoy the games and the fora. While you are at it, upload an avatar and make yourself at home!

Destroy him, my robots. xD

Welcome comrade!

You know nothing, GlorFindel. It's a part of the plan.
One ring to rule them all, One ring to find them, One ring to bring them all and in the darkness bind them.
And then, after that, GOG goes to Fire Mountain, Mount Doom, Orodruin — and you should know what happens next ;)