I can't read French but I think you download it onto your phone or something. With it, you can monitor your account aswell as individual characters. You can check your stats, what equipment you have on, your allignment status, what friends are online/offline, all guild information and possibly other stuff I haven't looked at.
On top of that, it gives the server status for all severs, has a handy encyclopedia where you can search for items and find out about them, shows the ladder for all servers, and possibly other stuff.
This thing is amazing! Though sadly it's only in French right now. BUT I did notice that in the options, there is a language selection thing, which might just have a choice of english later in the future! The link above gives you a fully interactive peek at what you can do with it.
I am going to feel bad if this was meant to be some big surprise and i'm spoilt it.
*~*~*~*WhAtEvEr YoU ReAd On ThIs ToPiC, YoU ShAlL FoRgEt WhEn YoU LeAvE iT*~*~*~*
There, now I shant feel so bad.