The only app of this kind is "SysApp Pusher" which looks to see if there's updates for the Nokia, Samsung, HTC apps. For all other apps, you just have to wait for the store to update and show you have an update or sometimes news about the update will come out on a site like WPCentral and if you go to the app in the store you'll see the update option even though your store live tile wasn't showing yet that an update was available.