Apps with 'Notification Center' feature

Ruppu is a mobile application that allows users to store and access shareable media directly from their smartphone notifications, simplifying the process of locating desired files.

A simple notification daemon with a GTK gui for notifications and the control center

“BuzzKill allows you to see the notifications you want to see when you want to see them and filter out those you don't.”.

iTunification makes it so you don't have to switch to iTunes again. You can see your music right where you are.When you play songs in iTunes or Spotify, iTunification gets the track's details and shows them in OS X 10.8 new Notification Center or Growl. Your choice!

Adds extra 'reminder' and 'DND' button(actions) to notifications. Reduces notification overload with a category-based notification system.

Hiss is an OS X app that forwards notifications from Growl enabled apps to Notification Center in Mountain Lion.

MountainGrowl - Growl Display Plugin for Mountain Lions Notification Center.

NowPlaying displays a notification whenever a track starts playing in iTunes or Spotify so you see the track's title and artist as soon as it starts.

A notification daemon/center for linux.

View the status of Time Machine right from your desktop or Notification Center.