The web calendar lets people store appointments, receive
reminders and share schedules with others.
It is tied in to Google's e-mail service, Gmail,
automatically offering to add the date information in a
message to the calendar.
The calendar is Google's latest effort to offer
all-purpose web services.
It plans to use the cash from the sale to fight off
stiff competition and stay ahead as the world's most
used search engine.
Google Calendar is part of its expansion into new
areas, pitting the search giant in direct competition
Yahoo has offered a calendar service since 1998 and
in October bought the event planning site, Upcoming.org.
Yahoo is currently the most popular web calendar
service in the US.
In response to Google's announcement, Yahoo said it
would release updates to its calendar service in coming
Google's service is designed to be easy to use, said
Carl Sjogreen, product manager for Google Calendar.
As well as being integrated with Gmail, the calendar
uses so-called natural language processing technology to
simplify how events are added.
It means that people can type an entry like "lunch on
Sunday 12pm" and the software will automatically add it
to the calendar.
"We enable the user to create multiple calendars,
share them with other people and overlay web calendars
back on the user's own calendar,"said Google Calendar
product manager Carl Sjogreen.
At the moment, the calendar works best with
Microsoft's Internet Explorer and Firefox. In the coming
months, Google aims to make it synchronise with Outlook
and mobile devices.