The IDEA:
Please build up a single, central calendar solution where any of your applications will interface by default to make it easier and more transparent to the users and administrators.

@All readers: if you find this a valid requirement, please don't forget to upvote this IDEA (top left of the message), as this will give Zoho a feeling of urgency.

The PROBLEM:
Almost any tool of Zoho One has its own calendar solution.

As a user, I have to sync any of these calendars with each other and any of them with my Outlook, Google, and Phone Calendars. The settings to achieve this are in different places and dialogs; thus hard ti find.
Even worse is that in most of Zoho One's tools, this is something that has to be done by the user itself and can't be done by the admin. There is not even a view for an admin to check which of the users have done the minimum required calendar configurations to do their jobs and to be able to do them right by not missing appointments or conflicting with events. This tends to mess things up!

On your end, I assume that you have hundreds of ours at the helpdesk, arguing with your users/customers about what's working and what is not intended functionality.

I think everybody agrees with the following thesis:

1. an individual in a company has only a specific time span to provide 

  a. postpone new things,

  b. postpone the planned things, or

  c. get rid of at least one of the two overlapping things

3. it does not matter which application brings up new meetings/appointments at a specific time. You must pick one option out of 2.a. ... 2.c.

Because of this, distributed calendars are crap and don't do any good to all of our businesses.

The SOLUTION:
The envisioned central Calendar solution will be assigned to the user the first time he registers to any of your tools, requiring a calendar functionality. From now on, any newly added/registered application will use the same calendar as this user.

We all will save on troubleshooting, trial & error, development, and helpdesks.... and we will never overbook or miss appointments/events/calls/meetings/conferences... you name it. 
And users will have only one calendar to sync with their non-Zoho calendars.

BTW: This is not a really NEW idea, as we all can name several services and platforms where this has been the standard for at least a decade.