Originally launched in 2003 as a digital delivery mechanism for Valve’s Half-Life 2, Steam has evolved into the most prominent digital distribution platform in the world. A Mac version has been available since 2010.
Many games in Steam’s catalogue are SteamPlay-enabled, meaning they can be bought once and used on both Windows and Mac systems (Call of Duty: Black Ops remains a notable exception). Steam also allows for other features, such as SteamWorks (an API which allows for online ranking, matchmaking, achievements and other features in supported games), Steam Workshop (a system for automatically adding user-created content and mods to games) and the Steam Overlay (which can be activated in-game by pressing shift-tab and provides access to chat and other functions). In 2012, “Big Picture” mode was added, allowing Steam to run full-screen via a gamepad, essentially turning the Mac into a games console.
Steam is also known for its frequent sales, whereby prices for games are typically cut by as much as 75% or more, as well as its published statistics.