Xbox SmartGlass. Finally on the App Store.
UPDATE: Ok, this is pretty piss poor. App behaves very much like the My Xbox Live app, in the sense where it doesn't feel as fluid as a typical iOS app does. Hangs a lot when loading, doesn't feel nowhere near as responsive as a native iOS app. Typical Microsoft crap. I'm using an iPad 3.
UPDATE 2: When you boot up Halo 4, Smartglass loads up Waypoint. Now, instead of hooking into Waypoint's APIs, SmartGlass just seems to be loading up a browser within the app. SmartGlass doesn't feel so smart.