WindowsPhoneHackerâ€™s Notification app was an achievement not only for what it did, which was collecting notifications from a variety of courses in a single app interface, but also for managing to get the app into the Windows Phone Store.
It seems this second achievement was not meant to last, with Microsoft apparently pulling the app from the Store.
WPH is aware that the app has been removed from the store, but is not explaining the reasons.
For existing users the app continues to function, but if you uninstall it you will unfortunately be out of luck.
We can only hope the app was pulled because Microsoft is planning to release their own unfinished notification manager, rather than because WPH violated some unwritten law.