Heathstone is a Competitive Card Game made by Blizzard, developers of hit games like Rock N' Roll Racing, The Lost Vikings, and some MMO I guess. That MMO has a universe -- Warcraft -- which is the theme of the card game, featuring famous enemies and characters from the franchise as well as new characters made solely for that series. Since it's release, Hearthstone has seen FOUR Adventure Expansions and FIVE Pack Expansions that drastically alter the meta of the game.
It's Available on PC, iOS and Android -- all cross compatible with one another.
Wild Players, bless your hearts.
Standard Players, we wish you luck in the hellish landscape of Quest Rogues, Pirate Warriors and Warp Mages.