Control access to particular pages, fields
Drupal has long had a variety of access control modules, to make it so you can easily control who can view or edit particular pages. There are actually several different layers of APIs to control this in Drupal core -- the modules generally provide a user interface to let you control access by content type, by tagging content with particular terms, through their position on a menu, or through a group. The Field Permissions module lets you control access to particular fields on an entity.