Growl for Windows - Growl for Windows is a Windows-compatible version of https://alternativeto.
FITTEVER - Fitness at your fingertips. Live fitness classes.
Notify OSD - Canonicals on-screen-display notification agent, implementing the freedesktop.
Classtra - Single platform for virtual, in-person, hybrid activities
Notifu - Notifu, a free open source pop-up balloon utility
SocialBoat.live - A real life Fitness game