Online game store Good Old Games, well known for their DRM-free distribution, have announced their own game client, named GOG Galaxy. Though details are scarce, what we do know is that you'll be able to play all your games offline, giving it a major boost over rival Steam, whose clunky offline mode very often doesn't allow all games to run. You also aren't required to update games before running them, and according to the video, there seems to be some form of integration with other game clients. Of course, I'm basing that off pictures of constellations, but I can hope.
If there actually is cross-play between GOG Galaxy and Steam, there will be a definite advantage for Galaxy compared to other competitors such as EA's Origin. Many people have most of their games on Steam, and forcing gamers to switch from something they like takes a miracle worker. More details are yet to come, but GOG Galaxy might be that miracle worker.