Update Monitor will inform you about iOS/OS X app updates even if you don't have installed these apps currently. Just add all your apps to your list of monitored apps within Update Monitor and it will look for updated apps each time you launch it. If an updated app is detected, Update Monitor will mark this app in the list of monitored apps, no matter how many apps are monitored.
Update Monitor shows release notes, images, descriptions, supported devices, and more for each monitored app.
Note: Now requires OS X 10.10 or later