Zenkit

The iCalendar add-on is a calendar subscription based on the open source iCalendar (.ics) standard to allow you to integrate your Zenkit calendar into other calendar apps such as iCal, Outlook, Google Calendar, etc. This calendar subscription is one-way (Zenkit -> external Calendar App). 

Enable iCalendar subscription add-on

To enable the iCalendar subscription add-on, click on the list name, then on "Manage Add-Ons". 

Click on "Add" next to "iCalendar". In the next window, pick which fields should appear in the destination calendar.
 Summary: The title of the event in the destination calendar.
Date: The date the event should occur on.
Description: The description text inside the event. To change which field is used for each of these sections, click on the name of the field.Once you're done, click "Enable" in the top right hand corner.

Add a saved filter to your iCalendar link

You can optionally add a saved filter to your link, so that only items that match that filter will be sent across to your external calendar. To add a saved filter, click on "None" under the Filter section and choose the filter you'd like to add:
A link with the condition to use the filter will appear underneath. Copy this link and add it to your calendar app.Note: You can generate this link for as many different saved filters as you like. Generating a link with a filter attached has no effect on the main subscription link. If you reset the link, you'll need to generate your filter links again. 

Add your Zenkit calendar to another calendar app

Copy the URL shown in the iCalendar Subscription add-on settings. (Note: the add-on has to be enabled for this to work.) This is the subscription URL you should use to add your Zenkit calendar to another calendar app.

Here's how you can subscribe to a calendar using various popular calendar apps:
Mac Calendar
iPhone or iPad Calendar
Outlook.com

Manage or Disable iCalendar add-on

To manage or disable the iCalendar subscription add-on, open the list settings by clicking on the list name, then click on "iCalendar Subscription" under the "Add-ons" section of the left panel. You can change the fields used to send data to the summary, date or description fields, as well as reset the iCal link to invalidate the old one. To disable the add-on, click on "Remove Add-On" at the bottom of this dialog. If you disable this add-on, the iCal link becomes obsolete. If you want to enable it again, you will have to add the subscription to your other calendar app again using the new link.

Your calendars are now accessible even without an internet connection. Even appointments that you have synchronized via iCal are now available offline.