Apps with 'Notification Center' feature

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

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

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!

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.

Turn banners off in System Settings and notifications still arrive in Notification Center. Nonja reads them from there and builds a list in your menu bar, grouped by the app that sent them. Nothing appears over your work.

A notification daemon/center for linux.

When Windows notifications stop working — no pop-ups, no sound, an empty Action Center, the unread count climbing while no banner ever appears — Microsoft's official escalation is to reset Windows or create a new user profile. WNF fixes the actual cause instead.

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

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