iCal or iCalendar was the first calendar application to offer support for multiple calendars and the ability to publish/subscribe calendars similar to RSS Feeds.
The user interface of this TYPO3 extension is based upon the PHP iCalendar project, available at www.phpicalendar.net. Many thanks to its developers for a great product to build upon.

One powerful feature offered by the Calendar Base is the ability to subscribe to external ICS or iCal feeds. For example this could allow you to import and export events or even subscribe a whole calendar with Mozilla Sunbird (Windows, Linux) or iCal (Mac).

If you have ever installed an extension like tt_news you won't have any trouble installing calendar base. The Extension is installed (and updated) using the extension manager in the backend and easily configured using flexform configuration like every modern TYPO3 extension.
Calendar items can be created/edited in the backend and in the frontend, thus being an ideal solution for intranets with many FE users.
Of course this extension can be extended by extensions. Existing extension for example give the possibility of showing news items in the calendar.