A good number of people are familiar with Fullmetal Alchemist, whether they've actually watched it or not. As far as anime goes, it's kind of a big-name series. And unlike other popular series (*cough* Dragon Ball Z *cough*) it's actually good. The story of the Elric brothers has seen a number of adaptations and spin-offs, so it was only a matter of time before one of those spin-offs got its own game.
FMA Battle is a relatively new collectible card game based on the "less old" Fullmetal Alchemist: Brotherhood series. Calling it a spin-off, however, isn't entirely accurate. The original show followed the manga (a.k.a the source material) up until about the halfway mark, then went off and did its own thing. Brotherhood sticks to the script, so to speak. So technically, the original anime series was actually a spin-off. Confusing, no?
Getting away from semantics and back to the game at-hand, FMA Battle is a free-to-play CCG set in the FMA universe. Players will construct their deck and customize a team of three alchemists while continually dueling with others online. Cards/characters will gain experience as they're used, earning new abilities as they get incrementally stronger. Of course, this is a freemium game, so deck expansion is limited unless players are willing to pony up some actual cash to buy new cards.
Free online multiplayer. Collectible cards. Fullmetal Alchemist. I think it's safe to assume this will find its niche pretty fast. If it sounds interesting, then why not check it out? It's currently on the App Store, and as I've previously stated (repeatedly) it's free.