Calendars can be shared using Horde if you are not using the Calendar and Contacts Server ( CCS) plugin. If you are using Calendar and Contacts Server and need to share access to Calendars you can use the steps in the How to share Calendars when Calendar and Contacts Server is installed article
- Log into the system user email account's Horde
- Select Calendar
- Expand My Calendars and click the pencil icon
- Select the sharing tab
From the sharing tab you can choose to make this calendar public or only allow specific users access.
If you need the CalDAV URL this can be found in the Subscription tab