Hearthstone is a free to play card game. Currently available on PC, MAC, iPad, Android and iPhone. Players must choose one of 10 types of heroes and then two of them will fight on the battlefield. The two opposing players have a deck of thirty cards each, from which they draw 3-3 cards at the beginning of the game, the second player can draw another card and receive a bonus card, The Coin. Players draw a card in each round and have one more mana until they reach 10 manas. The goal is to take down all thirty health points of the opponent’s hero with the help of various creatures, spells and weapons.
More details about the game here: https://playhearthstone.com/en-us
UEG game rules here: Heartstone rules