Content

1) the ability to easily get data into and out of the calendar (ical and maybe RSS)
2) the ability to show other TYPO3 content on the calendar (cal_ts_service)
3) the ability to easily add events to the calendar (cal_ajax)
4) the ability to define many types of complex recurring events (frequency, rdate, exceptions)
5) Exchange-style features. Meetings, resources, etc