Collect some cards!
If you are tired of waiting to play Hearthstone, an alternative card game has popped up on Steam for you to enjoy. Ubisoft's Might & Magic Duel of Champions as a free-to-play title on Steam with DLC card packs available for purchase.
You'll have to put up with uPlay's annoying login and overall terribleness to play, but for a free game I think you can deal with it. The game came out back in May, but I somehow overlooked it until the Steam release. I'm sure I'll end up wasting at least an afternoon playing it.