To join public multiplayer servers, a factorio.com account is needed, which then tells you to buy the game (again) or link it to a Steam account that owns the game. There is no such option for GOG. Without this you can't join public multiplayer servers and you won't get in-game updates. I'm on GNU/Linux and the version available for download is outdated. The newest version is currently only available for Windows. This means GOG users can't play on public servers, so you will get a worse game than anyone else. You will also not get updates on time. What a scam!
