Already available on the App Store, X-Men: Battle of the Atom [Free] is one of the legit countless free to play collectable card games out there. However, it's got some neat features that might make it worth a second look if you passed it up when it launched in mid-January. Namely, massive player versus player battles that actually require a bit of coordination and communication once you get deeper in:
I'm partial to games like SolForge [Free] when it comes to these free to play CCG's, and with a release of Hearthstone potentially right around the corner it's hard to get that excited for anything else... But it's still cool to see developers mixing the formula up and including new mechanics- Especially when tied with recognizable IP.