 Dota 2 is a free @-@ to @-@ play multiplayer online battle arena ( MOBA ) video game developed and published by Valve Corporation . The game is the stand @-@ alone sequel to Defense of the Ancients ( DotA ) , a mod for the 2002 video game Warcraft III : Reign of Chaos and its expansion pack , The Frozen Throne . Dota 2 was released for Microsoft Windows , OS X , and Linux in July 2013 , following a Windows @-@ only public beta testing phase that began in 2011 . Dota 2 is one of the most actively played games on Steam , with peaks of over a million concurrent players , and was praised by critics for its gameplay , production quality , and <unk> to its predecessor , despite being criticized for its steep learning curve . 
