Literally every other platform, Steam, Epic, consoles, even VR, are all cross play compatible with each other. For some reason, the GOG version can only be played with other GOG users. I had to buy another copy on Steam to play with my friends. Multiplayer adds a lot to the game, so the lack of this feature is a serious detriment to this version of the game. Don't buy this unless all your friends use GOG, or you intend to play solo.
