Square Enix is releasing three Final Fantasy XIII games under the name "Fabula Nova Crystalis." One is simply XIII, the other is Versus XIII, and the third is a mobile phone game named Agito XIII. We don't really know much about how they're all connected--obviously, Versus XIII is not a direct sequel to XIII, or we'd have seen familiar characters in each by now. But they're all going to be related in one way or another.