Three Microsoft Office features that are essential (or nearly so) for a mature calendar application:
1. Multiple notification defaults for invitations that are NOT yet accepted or even declined, e.g., an upcoming invitation decision (yes/no/maybe) may need to be made closer to that date, like the day before.
2. Reoccurring dates often fall on a specific day of the week, month, or year, e.g., U.S. national holidays like Thanksgiving, but also in business and associations.
3. Adjustable width (with pin) for left panel in Calendar, especially essential for smaller laptops such as Surface Go!

I cannot leave Microsoft Office behind without these important features.
Thanks!