GOG brought its Galaxy client out of beta with a 1.2 update featuring cloud saves, a frames per second counter, and many other new and improved features. These additions should make GOG's marketplace for DRM-free games even more attractive to anyone willing to try something besides Steam.
Many of Galaxy's new features are common to other clients. There are desktop notifications for game invites, friend requests, and messages; support for screenshots captured by pressing F12 in supporting games; indicators that show if an achievement is common or rare among GOG users; and more. You can enjoy many of these same features on Steam, or if you're a console gamer, the PlayStation 4 and Xbox One and their respective online services.
Not that GOG needed to reinvent the wheel, of course, and the company smartly incorporated all these whirligigs and doodads into the Galaxy 1.2 update. Many features (desktop notifications, achievements, and more) can be disabled. You can also limit Galaxy's bandwidth usage at certain times; decide on a per-game basis if you want to enable automatic updates; and view notifications, the FPS counter, and online chat via an in-game overlay.
All those options should make it easy for you to configure Galaxy to your liking, or you can just play games purchased from GOG without ever installing Galaxy on your system--the company said that "GOG Galaxy will never be mandatory." Use it, don't use it, GOG titles don't care either way. That, and the fact that DRM-free purchases mean you don't need an internet connection to play a game, makes GOG more flexible than some other sellers.
Still, it's clear that GOG would like you to at least experiment with Galaxy. The client offers crossplay support that lets you join your friends in multiplayer games even if they use Steam instead of Galaxy, and it offers access to the same games as the GOG website, including those from the Steam Early Access-inspired "Games in Development." (GOG Connect, which lets you import Steam games to your GOG library, is site-only, however.)
You can download Galaxy 1.2 via GOG's website. The client is available for Windows 7 and later as well as macOS 10.8 and newer. GOG said a "Linux version of our client is planned eventually" but that it doesn't "have an expected release date right now." You can also learn more about GOG's vision for Galaxy in the video below.