Platypus - Realtime server monitoring and reporting
Snarl - Snarl is a notification system for Windows.
Monitornator - Server monitoring made simple
Notifu - Notifu, a free open source pop-up balloon utility
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Notify OSD - Canonicals on-screen-display notification agent, implementing the freedesktop.