From the interviews with Yoshi-P, the app (called Libra Eorzea) is going to feature very detailed information on a variety of game aspects, almost like a wiki or strategy guide. While most games rely on the player community to produce such a database, Yoshi-P explained he wanted to provide a convenient, officially-developed tool for players, partly as a way to say thanks to all the supporters.

A link: http://www.dualshockers.com/2013/08/...-will-be-free/