Update: Hearthstone is now in open beta in Europe as well.
Original (1/21): Have you been wanting to give Hearthstone a shot but couldn't? All your Battle.net friends were playing it, but you never seemed to get a beta invite. If this is you and you weren't flagged in the last wave of closed beta invites for Blizzard's collectible card game based off of the Warcraft universe, have no fear! Hearthstone: Heroes of Warcraft is now in open beta!
Everybody in North America can now download Hearthstone through Blizzard's Battle.net app, which also serves as a launcher for World of Warcraft, Diablo III, and Starcraft II. Europe and other regions will have to wait a little longer, but Blizzard aims to have open beta available for everyone by the end of the week.
Remember that this is only open beta, not a final release. Though already highly polished, the game still has bugs, and server stability has been an issue in the past for Hearthstone. If servers run into trouble again, open beta may have to be closed off for a bit until everything is back under control. If that happens, feel free to browse our developing NeoWiki for more information while you wait patiently to get back in.
A final release date will be announced at a later date, but everyone that's participated in either open or closed betas will be able to retain their card collections when the game does get released. Android and iOS versions are currently in development according to a brief statement from Blizzcon in November, though no additional information is available on that front just yet.