Google Calendar now lets you add a message when you change an event
Google Calendar gets a new useful feature. When you change or delete an event, a dialog box now pops up that allows you to attach a short message to the event to explain why you are making the change and what’s changing. On the event page in Google Calendar itself — and in the email that alerts your guests of the change — that message will then appear at the top of the event details section. The new dialog box appears automatically, so far more people will now explain their changes than before. This new feature is now rolling out to all G Suite users and should be available to everybody (no matter whether their admins have them on the rapid release or schedule release schedule) within the next three days.
Google Calendar alternatives are: Zoho Calendar, Yahoo Calendar, MS Outlook