Steamworks is described as 'free suite of tools available to any developer to use in their game or software on Steam'. There are seven alternatives to Steamworks, not only websites but also apps for a variety of platforms, including Windows, Linux, Mac and SaaS. The best alternative is CrossBrowdy, which is both free and Open Source. Other great sites and apps similar to Steamworks are Unity Multiplayer (Paid), Photon Engine (Freemium), mod.io (Free) and SocketWeaver (Paid).
Global cross platform multiplayer game backend as a service (SaaS, Cloud) for synchronous and asynchronous games and applications. SDKs are available for android, iOS, .NET., Mac OS, Unity 3D, Windows, Unreal Engine, HTML5 and others.
mod.io is an open platform for hosting mods created by the team behind ModDB.com and IndieDB.com. It can be integrated in-game using the REST API, C/C++ SDK or engine plugins for Unity, Unreal Engine and GameMaker.
SocketWeaver offers: 1. Lobby clusters in North America, Europe, and the Asia Pacific. 2. Game servers on a global scale. 3. Unity SDK that tightly integrated into the Unity Editor. 4. 20GB Free data (Renewed monthly).
With the Xbox Live Creators Program, anyone can integrate Xbox Live into their title and publish to Xbox One and Windows 10. With Xbox Live you can create a connected game experience that will give gamers even more reasons to keep playing.