hinti21: Do you know if it can be done to use both steam and gog overlay to get achievements in both clients (i own the game in both).
The overlay has nothing to do with achievements (achievements
were implemented on Galaxy long before the overlay after all). And whether a game can unlock achievements on both platforms at once really depends on a game's particular implementation of these two APIs. Your best bet would probably be to install the game via Steam, then
import it to Galaxy and launch it via Galaxy. But frankly I have no idea what's gonna happen in this case because as I said, it depends on each game's particular implementation. With one game I've seen achievements get registered
only to Steam even though I was running it through Galaxy.