Create groups with private content.
There are lots of additional modules with extra features.
The UI can be hard to work with. Modules or custom code are needed to streamline it.
ECA might be a good combination.
Group content
Content can be contained within a group.
Enable Group Node (gnode) module.
Roles and permissions
Groups can have custom roles/permissions
Recommended
Yes
Module page
Stability
Secure
Resources
Project updates