Snarl - Snarl is a notification system for Windows.
Pusher Beams - Send push notifications programmatically at scale
Notifu - Notifu, a free open source pop-up balloon utility
Mentioned By - Learn when your site is mentioned by other sites for free
Notify OSD - Canonicals on-screen-display notification agent, implementing the freedesktop.
Now Push Notify - iOS does not support browser notifications today, but Now Push Notify makes this possible.