Search giant Google today introduced a free, web-based calendar service, which allows users to schedule events and share them with others.

Google Calendar allows users to drag and drop events from one calendar to another. The tool is sculpted in Javascript and XML but also uses Google’s natural language processing technology to simplify event entering.

Users can type in events such as “pub 7pm tonight”, and the calendar will automatically schedule the event, allowing you to make it private or available for viewing by friends or even the whole web.

The calendar is also highly integrated with Gmail, searching emails for mentions of events an asking the user if they would like them to be automatically added to the calendar.

Although the Google Calendar is a direct challenger to the likes of Yahoo Calendar, Google is reportedly allowing interoperability with the two services so events can be shared.

Google is also understood to be working on interoperability with Microsoft Outlook and a number of mobile device calendars such as the Palm Treo smartphone.