I'm pretty excited about the product. Our hope was that it would really be the first calendar product ubiquitous enough to really get people using calendars in a big way, so wide-scale use was definitely one of our biggest goals. Some features that help with that:
- Event extraction. Google Calendar will scan your Gmail inbox for messages that contain some structured event information, extract that information, and place a link on the side of the message allowing you to add the extracted event to your calendar. This works with both free-form text and Outlook-style meeting invitations with an actual iCal attachment.
- Quick add. Near the top-left corner of Google Calendar is a "Quick add" link. You can use it to enter free-form text describing an event, and the corresponding event will be created for you.
- iCalendar and XAPI (CalRSS) feeds. Every calendar you create on Google Calendar can have public and private iCalendar and CalRSS feeds to make integration with 3rd-party applications (like Evolution, Apple iCal and Mozilla Calendar) easy. Google Calendar can also subuscribe to iCalendar feeds and import iCalendar files.
- Outside organisers. Using the iMIP standard, responding to meeting invitations send from Outlook, Hotmail, and Yahoo! Calendar works properly.
The features I worked on, for the morbidly curious:
- Calendar sharing and ACLs
- Multiple calendars and new calendar creation (this is definitely something you should use; you can create multiple calendars to have, say, a "work" calendar and a "personal" calendar)
- Some of the calendar feed stuff
- Some of the recurrence stuff
- General backend stuff