CCalendar - The approved-popular online-group-calendar:

• Common appointment-management location-independent by web - from any arbitrary browser
• Automatic appointment-reminder by e-mail at once / daily / weekly / monthly
• Management of recurring appointments and appointment-variants!
• Appointments in day-, week-, months-, year-views.
• User-management with individual rights-management
• Modules to display your public appointments on your existing homepage - very simple by module as list, ticker, xml, iCalendar or IFRAME available.
  (You just need to store your appointments in one place. Your homepage will be kept up-to-date fully automated!)
• Encoded data transfer by SSL-server , additional backup-server and further
  data-privacy- and data-security-protections - no data assignment to other systems!
• Booking-module for booking resources by external users,
  as well as additional compact Seat-reservation-system for easy reservation and booking.
• Appointment-finder - find the best possible appointment for all participants by automated requesting
• New: CManager: The optional integrated groupware extension: Person management, ToDo lists, Mailing lists, ...
• Gateway for synchronisation with MS-Outlook
• App for using with Smartphone    
• iCalendar (.ics / .ical) data-gateway for including your appointments into external calendars like MS-Outlook, Google Calendar, Smartphones (iPhone, Android, Windows Phone, ...), und many others
  as well as reverse for displaying external appointments in CKalendar
• Integrated document-storage und appointment-appendix
• Data import- und -export-possibilities for further processing of your appointments in MS-Excel
• XML-Gateway
• All 50 days free and without commitment for testing!
  And afterwards for a very cheap price with a discount for non-profit organisations!
• and much more ...