http://en.wikipedia.org/wiki/Steam_%...nt_delivery%29 (or if you're too lazy to click here's what it says V)

Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation. It is used to distribute games and related media online, from small independent developers to larger software houses; in October 2012, Valve expanded the service to include non-gaming software. Steam provides the user with installation and automatic management of software across multiple computers, 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, Steamworks, that developers can take advantage of to integrate many of Steam's functions within their software products, including copy protection, networking and matchmaking, in-game achievements and micro-transactions, and support for user-created content through Steam Workshop. Though initially developed for use on Microsoft Windows, the client has expanded to include OS X and Linux versions, and clients with limited functionality on the PlayStation 3 console and for both iOS and Android mobile devices. In addition to being a central hub for gaming software, Valve has created a version of Steam with altered functionality to be used in schools for educational software, including a modified version of Portal 2 for teaching science and critical thinking lessons.

As of December 2012, there are nearly 2000 games available through Steam,[5] and 54 million active user accounts.[6] As of January 2013, Steam has seen over 6.6 million concurrent players.[7] Steam has an estimated 50–70% share of the digital distribution market for video games.[8][9]

The Steam logo is a stylised left-side fly-crank and rod from the Walschaerts valve gear of a steam locomotive.