Rumors about Google's plans for an online calendar service have circulated for more than a year. Today, Google Calendar beta went public, sporting an uncluttered interface and the potential for users to mash it up to their liking. Yahoo Calendar is the leading service in this space, but an open application programming interface (API) isn't available--yet. The AJAX-based Google Calendar beta already works with XML and iCal standards. Not only can you create multiple calendars, you can also import them from Microsoft Outlook.
Your own Google Calendar is private by default, but you can open it up for strangers or friends. Say your favorite art gallery, theater, or book club uses a compatible calendar service. You could instantly add their events within your personal Google Calendar so that you won't miss the latest parties around town. This service is also designed to flag events within Gmail messages in case you'd like to ink them into your calendar. Color coding helps to keep things straight. You can export your schedule via RSS, then read the feeds from a third-party newsreader.
Similar to Outlook and Evite, Google Calendar beta also 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.