Sync between different Civicrm dbs
I don't believe there is any shared code for this currently. We are working with a client in Aus to build such a system for them which would involve sharing (pushing/pulling) data from the 'parent' crm to various 'child' crm databases.

If you need a solution then we may be able to extract the work we have done that relates to just the features you need but would clearly need to charge and would provide an estimate if you were interested. You can contact me via https://www.fuzion.co.nz/helping-those-who-do-good-do-better or https://chat.civicrm.org/civicrm/messages/@petednz-fuzion