Looking to play on my iPad with my friend who has a PC. I think Hearthstone will work (will try later and confirm). Are there any other games people are aware of. It might be nice to have a centralised list. Other ones I can think of are: Frozen Synapse Words with Friends Space Hulk Cube men 2 Hero Acadamy Also I think the upcoming Godus will also be cross platform.
Im pretty sure shadowgun deadzone, they have pc servers now so if you two make an account and invite each other then you two can play
There are quite a few games with cross platform Mac / iOS multiplayer through Game Center, though PC support definitely seems less common.
List updated (feel free to add yours !) - Hero Siege (soon in a update) - Monster Madness Online (not out yet) (from Dungeon Defenders devs also cross platform !) - Machines at War 3 (RTS premium) - Thief Town (not out yet this summer)
These games by slitherine have cross platform multiplayer Battle academy Panzer corps Commander the Great War