I have two organisations; both are CiviCRM users. One is the main office and in charge of membership management and membership fees. The other is the local branch and organises events and manages the volunteers.
The main office has a superset of the contacts of the local branch. The local branch has more information, for example, event participation and volunteer details.
The configuration of the two CiviCRM instances are very different but makes sense to exchange information. For example change in the email address in the local branch is of interest for the main office. A new member must be reported to the local branch.
Any tips, what is the best way to do this. Maybe someone has created an extension that can be used, as an example?