Please rate, comment, and subscribe. Dota 2 is a free-to-play multiplayer online battle arena (MOBA) video game developed and published by Valve Corporation. Released for Microsoft Windows, OS X, and Linux in July 2013, following a Windows-only public beta testing phase that began in 2011, the game is the stand-alone sequel to Defense of the Ancients (DotA), a mod for Warcraft III: Reign of Chaos and its expansion pack, The Frozen Throne. Dota 2 utilized the original Source engine until it was ported to Source 2 in September 2015, making it the first game to utilize the new engine. Dota 2 is played in matches between two five-player teams, each of which occupies a stronghold in a corner of the playing field. A team wins by destroying the other side's "Ancient" building, located within the opposing stronghold. Each player controls one of 110 playable "Hero" characters that feature unique powers and styles of play. During a match, the player collects gold, items, and experience points for their Hero, while combating Heroes of the opposite team. Development of Dota 2 began in 2009 when IceFrog, lead designer of the original DotA mod, was hired by Valve. Dota 2 was praised by critics for its gameplay, production quality, and faithfulness to its predecessor, despite being criticized for its steep learning curve. The game is one of the most actively played games on Steam, with a peak of over a million concurrent players in February and March 2015..