Add a very powerful Calendar system to your website

This has got to be one of the most powerful, and free, calendars you can add to your website.

From the site:
"WebCalendar is a PHP-based calendar application that can be configured as a single-user calendar, a multi-user calendar for groups of users, or as an event calendar viewable by visitors."

Features

• xhtml/css compliance
• Multi-user support
• 29 supported languages: Basque, Bulgarian, Chinese-Big5, Chinese-GB2312, Czech, Danish, Dutch, English-US, Estonian, Finnish, French, Galician, German, Holo-Big5, Hungarian, Icelandic, Italian, Japanese, Korean, Norwegian, Polish, Portuguese_BR, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish, Welsh
• Auto-detect user's language preference from browser settings
• View calendars by day, week, month or year
• View another user's calendar
• View one or more users' calendar via layers on top of your own calendar
• Add/Edit/Delete users
• Add/Edit/Delete events
• Repeating events including support for overriding or deleting (exceptions)
• Configurable custom event fields
• User-configurable preferences for colors, 12/24 time format, Sun/Mon week start
• Online help
• Checks for scheduling conflicts
• Email reminders for upcoming events
• Email notifications for new/updated/deleted events
• Export events to iCal, vCal or Palm
• Import from iCal, vCal or Palm
• Optional general access (no login required) to allow calendar to be viewed by people without a login (useful for event calendars)
• Users can make their calendar available publicly to anyone with an iCal-compliant calendar program (such as Apple's iCal, Mozilla Calendar or Sunbird)
• Publishing of free/busy schedules (part of the iCal standard)
• RSS support that puts a user's calendar into RSS (WebCalendar 1.1+)
• User authentication: Web-based, HTTP, LDAP or NIS

Link:
http://www.k5n.us/webcalendar.php