With its just-fielded Google Calendar service, Google is going head-to-head with a number of other companies with lengthier histories in this space, including archrival Microsoft.

Microsoft has offered calendaring as part of Outlook and Hotmail for years. Recently, Microsoft added more calendaring offerings to its stable. It introduced a new calendaring facility that it is baking into the beta and final releases of Windows Vista, as well as new calendaring functionality as part of Windows Live Mail, the successor to Hotmail known by the code name "Kahuna."

There's also a third-party-developed Windows Live gadget called "Windows Live Calendar" that is available for download from Microsoft's Gadget Gallery site.

"Microsoft has a long history and deep investments in calendaring," said an MSN spokesman. "We have had consumer calendaring services with MSN for years, as well as consumer and enterprise level calendaring with Outlook and Exchange."

Like other AJAX calendaring applications, the calendar that is part of the Windows Live Mail beta includes basic sharing and alert capabilities, MSN officials said. Google Calendar, for its part, features shared contact lists, cell-phone text notifications and built-in search, according to Google officials.

"We've simultaneously been improving our Calendar to complement our suite of Windows Live services," the MSN spokesman said. "Calendaring is an area where we will innovate, so stay tuned."

On Microsoft's Windows Live Web privacy page, Microsoft already has an entry for "Windows Live Calendar and Contacts," describing the pair as a place for storing "contact information you enter there about yourself and others including calendar appointments, email address, first and last name, nickname, home address, work address, phone number, and birthdate. You may view, edit, and share that information with your friends and acquaintances."

MSN officials said in March that the company is moving toward making a key set of its Windows Live services -- starting with Windows Live Contacts, Identity and Storage -- the crux of a Windows Live developer platform. Microsoft is encouraging programmers to build on top of these when devising new Windows Live services.

On the Vista front, Microsoft also is focusing on calendaring. Microsoft has embedded into the latest Vista test builds a Windows Calendar that allows users to share their calendars, as well as publish and subscribe to calendar data.

"Windows Calendar is fully compatible with the popular .iCalendar format, which lets you import and export calendar information to and from other applications and websites," according to Microsoft's Vista Web site.

"Windows Calendar used in conjunction with Windows Live Calendar will probably offer some unique benefits," said Matt Rosoff, an analyst with Directions on Microsoft. "For example, you will probably be be able to store all your appointments in the local Windows Calendar, then automatically upload them to the Live Calendar site so you can access them from anywhere, and share them with others.

"This would fit in with Microsoft's general Windows Live strategy, in which Live services can work on their own, but have added functionality when used in conjunction with Vista," Rosoff added.