Hi
I assume you need a separate application that combine
- Data
- Functionality
From Zoho and Vtiger.
For Data, we can simply use the vtiger API and Zoho Api. Please refer the onlin edocumentation of both of these API to understand the restrictions and constraints.
Sharing functionality might be a serious job, if you like to re-use the core functionalities of both CRM, such as lead conversion or Sales order to invoice.
Anyway , please provide the detailed requirements, so I am able to provide an actual estimation.
Thanks
Sutharsan Jeganathan