Steam is a digital distribution platform developed by Valve Corporation offering digital rights management (DRM), multiplayer gaming and social networking services. Steam provides the user with installation and automatic updating of games on multiple computers, and community features such as friends lists and groups, cloud saving, and in-game voice and chat functionality. The software provides a freely available application programming interface (API) called Steamworks, which developers can use to integrate many of Steam's functions into their products, including networking, matchmaking, in-game achievements, micro-transactions, and support for user-created content through Steam Workshop.
Though initially developed for use on Microsoft Windows, versions for OS X and Linux operating systems were later released. Applications whose main functions are chatting and shopping have also been released for iOS, Android and Windows Phone mobile devices. The Steam website also replicates much of the storefront and social network features of the stand-alone application.
As of September 2015, there are 6,464 Windows games, 2,323 OS X games, and 1,500 Linux games available on Steam. The service has over 125 million registered accounts. Steam has had as many as 12.5 million concurrent users as of November 2015. The Steam platform is considered to be the largest digital distribution platform for PC gaming; in November 2009, Stardock estimated it at 70% and then later, in October 2013, it was estimated by Screen Digest that 75% of games bought online were downloaded through Steam. In 2015, users purchased titles through Steam or through Steam keys from third-party vendors totaling around $3.5 billion representing 15% of the global PC game sales for the year, based on estimations made by the tracking website Steam Spy. The success of the Steam platform has led to the development of a line of Steam Machine micro-consoles and personal computers meeting minimum specifications, and SteamOS, a Linux-based operating system built around the Steam Client Server.