Blizzard's free-to-play card battler Hearthstone has reached a significant player milestone.
Hearthstone: Heroes of Warcraft, as it is officially called, now has over 20m registered players. It previously had hit 10m in March but has since then added to its PC and Mac version by launching on iPad.
An Android and more general iOS release is expected any time now, and certainly by the end of the year.
Hearthstone is considered one of the best examples of F2P, allowing non-paying players to fully get involved in the action with no penalties. As the title is so excellently crafted and immensely playable, however, Blizzard is most likely making a fortune from its IAPs.