A pop up notification (on top of whatever software that is open) is nice, but if there is the possibility to add a specific sound to it, I'd be more excited as I might be in the office but not working directly on the computer (yes, it is still possible! 😉).

It could draw my attention whatever I am doing, knowing : "that is a CU (calendar) notification, it is time to start / end x, y, z, I should check".