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
Truepush - Unleash limitless possibilities with Truepush and save up to $600 monthly. Free up to 10K Subscribers on all features.
Notify OSD - Canonicals on-screen-display notification agent, implementing the freedesktop.
F5Bot - F5Bot will send you an email whenever your brand, product, or keyword is mentioned online.