iCalendar and WebDAV
iCal supports the iCalendar standard and has been designed to allow data exchange between other iCalendar products like Apple's iCal calendar and Google's calendar. iCal will function as a WebDAV server which allows applications to Publish calendar data directly to the system. This iCalendar Data Exchange page provides details on the workings of this feature.

Custom Fields (Optional Feature)
Custom Fields can be defined for events; you can specify any number of data fields for all events in a calendar. Each field has an associated input type, used when adding new events: single-line text, multi-line text, pulldown menu, multiple-choice list, or checkbox. You can specify the options for the pulldown menus and multiple-choice lists, as well as defaults for each field.

RSS Feeds
The details of the calendar can be pulled as an RSS Feed.

Double-click to add
You can double-click to add a new event in a popup window. (Click in date headers in the Block View, in the date or day or blank cells in the List View.)

Other Features

• Solid banner bars can be selected to display multi-day events.
• Cascading Style Sheets define the look of all menus and entry forms.
• Color names can be used on the event entry form. New easier color picker.
• The block view can define scroll bars for the daily blocks.
• A more descriptive and readable log file.
• A new option to delete all calendar events.
• All individual calendar entry fields can be defined as viewable or hidden on the entry form.
• Double Clicking on events from an included calendar will take you directly to the edit form for the event.

Take a look at the Change History if you're interested in older versions of iCal.