The first three games in the Warcraft series, including their .expansion packs, were all released on both the PC and Macintosh. All of these games were of the real-time strategy genre. Each game proceeded to carry on the storyline of the previous games and each introduced new features and content to improve gameplay. Warcraft III was the first game in the series to feature a Collector's Edition, which all subsequent games have released as well. Warcraft II was the first game in the series to feature play over the internet using .Battle.net, although this was not included until a later release of the game. Warcraft II was also the first in the series to be re-released as a "Battle Chest", a bundled copy of the game containing both the original and expansion. Warcraft III and World of Warcraft also have both had "Battle Chests" released for them subsequent to their initial release. The "Battle.net" edition of Warcraft II was also the first to introduce the use of CD keys to the series, requiring each user online to have their own copy of the game in order to be able to connect. However, a CD key is not yet required to play via a Local Area Network, although speculation is that future games in the series will do so, as another product in Blizzard Entertainment's portfolio, StarCraft II, is doing so by removing the option for using LANs altogether, requiring the use of Battle.net.[10] In 1998, an adventure game in the series, Warcraft Adventures: Lord of the Clans, was announced as being cancelled, having been previously delayed from a 1997 release. In 2004, Blizzard Entertainment moved the series away from the real-time strategy genre and released World of Warcraft, an MMORPG. Requiring a subscription fee to be paid to play, it also introduced regular additional content to the series in the form of patches. World of Warcraft quickly gained much popularity worldwide, becoming the world's largest subscription-based MMORPG. They reached a peak 12 million subscribers worldwide.[11] World of Warcraft has had five expansions as of 2014. During the production of StarCraft II: Wings of Liberty, Blizzard co-founder Frank Pearce stated that "If there’s a team that’s passionate about doing another WarCraft RTS, then that’s definitely something we would consider. It’s nothing that we’re working on right now, we have development teams working on Cataclysm, StarCraft II: Wings of Liberty, Diablo III, and when those teams are all off the projects they’re working on, they’ll be intimately involved in the discussions about what’s next." In 2013, Blizzard announced a new online free-to-play trading card game titled Hearthstone: Heroes of Warcraft, with the beta being available in summer of 2013.[12] In March 2014, Hearthstone was officially released. In addition to the free-to-play basic gameplay Hearthstone also contains fee-based features like extra card packs, a special tournament mode or additional restricted matches against computer opponents.