The Steam platform is considered to be one of the largest digital distribution platform for PC gaming, and was estimated by Screen Digest to have 75% of the market space in October 2013. In 2015, users purchasing 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. By the end of 2015, the service had over 125 million registered accounts, with 12.5 million concurrent users. The success of the Steam platform has led to the development of a line of Steam Machine micro-console, as well as SteamOS, an in-house fork of the Debian operating system. As of February 2015, Steam has over 125 million users.