A highly specialised plugin that allows site admins to limit users to only being able to see events in categories and calendars that they are authorised to create events in.  Please do NOT install this plugin unless you understand what it does - many users install this and find that site visitors cannot see any events.  That is exactly what it is designed to do - visitors can ONLY see events on pages where they can create events.

The latest versions offer an  optional whitelist of categories or calendars where these viewing restrictions DO NOT apply.  So you can have a mixture of public and restrited access categories/calendars.  You can find the calendar ids by viewing the manage events page in the bckend of the site and then view the page source and search for icsFile in the HTML.