StarCraft is a military science fiction real-time strategy video game developed by Blizzard Entertainment. The first game of the StarCraft series was released for Microsoft Windows on 31 March 1998. With more than 11 million copies sold worldwide as of February 2009, it is one of the best-selling games for the personal computer. A Mac OS version was released in March 1999, and a Nintendo 64 adaptation co-developed with Mass Media Interactive Entertainment was released on 13 June 2000. Work on the game started shortly after Warcraft II: Tides of Darknesss release in 1995. StarCraft debuted at the 1996 E3, where it was unfavourably compared to Warcraft II; as a result, the project was entirely overhauled and then showcased to public in early 1997, receiving a far more positive response. StarCraft has had its storyline adapted and expanded through a series of novels, the expansion pack  and two authorized add-ons. The game's sequel, StarCraft II: Wings of Liberty, was released in July 2010, with a further expansion pack, StarCraft II: Heart of the Swarm, expected in 2012.