The Xfce developers are busy porting Xfce applications and components to GTK3, and in the process, they are also adding new features.

"Do not disturb", a much requested feature, landed in xfce4-notifyd 0.3.4 (the Xfce notification daemon) recently. Using this, you can suppress notification bubbles for a limited time-frame.

NoNotifications is an Ubuntu indicator for temporarily suppressing NotifyOSD (which is used by Unity) notifications. This can be useful for presentations, when working, and so on, to prevent unwanted notifications.

Sukochev Roman's (Leolik) patched NotifyOSD PPA adds extra features on top of the Ubuntu NotifyOSD notifications, like closing the notifications on click, option to move the notifications to a different screen corner, configurable colors for both the notification background and text, and much more.

I recently stumbled upon an interesting tiny old script which can translate any text you select. After highlighting the text, be it in a web browser, Libreoffice or PDF document and so on, upon using a keyboard shortcut, its translation is displayed in a desktop notification.

The application supports almost all Android applications and you'll get notifications when you get a call, a SMS or WhatsApp message, Facebook notifications and so on. From the LinConnect settings you can select which applications can send notifications to your desktop so you don't get flooded with useless notifications.