Subsites with shared components data and independent core
You have a website http://master.com and want to have a subsite http://slave.com or http://slave.master.com which has own database data but shares certain components with master site.
Subsite should be created as parked domain for master site in your hosting panel first.
Both master site and subsite will use own database tables and hence have different separated contents.
But MightySites allows you to share preferred database tables for each site on individual table basis or per-component basis. You will be able to manage component from backend panel of master site or slave site and component's database data will be always same in all sites because database tables of master site will be used in both sites.
I.e. slave site can share users and community extension database data with master site.
Shared components can be managed from any site. All other contents are managed from own backend of each site as usual.
Installing/updating components and Joomla update are performed in each site separately. Usually update of shared extension can be performed in any site only once.