Growl for Windows - Growl for Windows is a Windows-compatible version of https://alternativeto.
Zoom - Equip your team with tools designed to collaborate, connect, and engage with teammates and customers, no matter where you’re located, all in one platform.
Notify OSD - Canonicals on-screen-display notification agent, implementing the freedesktop.
WebEx - Cisco WebEx Web Conferencing, Online Meetings, Desktop Sharing, Video Conferencing
Notifu - Notifu, a free open source pop-up balloon utility
GoToMeeting - GoToMeeting is a web conferencing service offering a range of services which are available on Mac, PC, iOS and Android devices.