The Google Calendar beta is like having a shared Microsoft Outlook calendar online so that friends and colleagues can see upcoming events. The Google Calendar beta has an uncluttered interface and the potential for you to mash it up with other data sets to your liking, as fans of Google Maps have done.
The AJAX-based Google Calendar beta works with XML, iCal and CSV standards. Yahoo Calendar is the leading service in this space, but an open API isn't available (yet), so don't expect any Yahoo mashups at this time. Google Calendar lets you import calendars from Microsoft's Outlook, and more integration with Outlook is expected.
Your own Google Calendar is private by default, although you can open it up for strangers or friends. Let's say, for example, your favourite art gallery, theatre or book club uses a compatible calendar service; you could instantly add its events within your personal Google Calendar so that you won't miss anything. This service is also designed to recognise events within the text of Gmail messages and flag them in case you want to ink them into your calendar. Colour coding helps to keep things straight. You can export your schedule via RSS, and then read the feeds from a third-party newsreader.
Similar to Outlook and Evite, Google Calendar beta lets you send invitations to anyone -- even to people who don't use Gmail. Event reminders, including SMS updates, are designed to keep you on your toes. Can't remember a lunch date? Search the calendar fields.
