justanoldgamer: I am not a multiplayer gamer but I am curious at how does it permit playing with gamers who use other clients?
My guess is it doesn't actually let GOG client and steam client talk, but rather has a way of cutting the steam client out of the picture entirely when appropriate. Pure speculation here (and may not be anything like what GOG is actually planning but is at least plausible):
1. It only works if the game is coded against the GOG Galaxy API. (Currently existing games on steam will not be able to play against GOG Galaxy enabled GOG versions of those games -- the game's devs would have to release a new version of their game
on steam that has GOG Galaxy support enabled.)
2. The GOG Galaxy API is actually two implementations underneath -- one implementation that knows how to talk directly to GOG's servers, the second implementation that knows nothing of how to talk
directly to steam's servers but does know how to translate the GOG Galaxy API calls into appropriate Steam API calls. (So devs don't have to code for both GOG Galaxy and steam -- they just code to GOG Galaxy and get both automatically. My reason for suspecting this is how hard it would be to get devs to code against two APIs, though it's also possible GOG has just made their API look pretty much exactly like steam's and then the effort isn't so much. Another reason for suspecting it is that it allows much better integration -- games could in theory show both available players on GOG and steam at the same time, and the game code wouldn't need to care about which is which.)
3. When a Steam player wants to play against someone on GOG, they would have to use GOG's matching service (though depending on how well it's integrated, they may not realize they are using GOG's matching service in addition to steam's). GOG's matching service will set up any GOG Galaxy enabled game for any set of players, as long as at least one of those players has a valid GOG key.
justanoldgamer: Will the games already in the GOG library be updated to be able to use Galaxy?
I would assume that's mostly up to the devs/publishers of the games. (The kind of reverse-engineering that is otherwise required is a bit of a pain, though it might be worth it if there are, say, 100+ games that rely on something like GameSpy and GOG only had to muck with it once to get all of those games working.) One thing GOG Galaxy might do is provide the ability to act as a VPN (in which case most games with pre-existing LAN support would probably be able to use that without being updated at all -- just run the GOG Galaxy client as a separate process to meet up and get the VPN going).
I'm not really expecting to see much in the way of concrete answers from GOG in the short term. GOG knows its customers can turn into a giant whack-job mob on a moment's notice if GOG does something they don't like, so they may be testing the waters here and seeing what people expect and what they wouldn't accept
before they put all of the coding hours into the implementation.
