Calendar Server

There are a variety of options for a Calendar Server:

• Calendar and Contacts Server -aka Darwin Calendar Server, is the open source version of the CalDAV and CardDAV servers that Apple includes with Mac OS X Server. It can be enabled on the Snow Leopard and Lion versions of OS X, and has also been ported to FreeBSD and Linux.
• SabreDAV is an open source WebDAV server built in PHP. It is an implementation of the WebDAV protocol (with extensions for CalDAV and CardDAV), providing a native PHP server implementation which operates on Apache 2 and Nginx web servers.
• DAViCal is a server for calendar sharing. It is an implementation of the CalDAV protocol which is designed for storing calendaring resources (in iCalendar format) on a remote shared server.
• Radicale aims to be a light solution, easy to use, easy to install, easy to configure. As a consequence, it requires few software dependencies and is pre-configured to work out-of-the-box.
• Mod_caldavis an Apache module implementation of CalDAV which defines extensions to the (WebDAV) protocol to specify a standard way of accessing, managing, and sharing calendaring and scheduling information based on the iCalendar format.
• Baïkal is an open-source, lightweight PHP+SQLite CALDAV+CARDDAV server based on SabreDAV.

Microsoft Outlook
Bynari WebDAV Collaborator- a powerful plug-in for synchronizing your CalDAV calendar and/or CardDAV contact data to Outlook. Whether you are a Microsoft Exchange user that needs to synchronize your Gmail calendar or a Zimbra user that needs more flexibility in Outlook, the WebDAV Collaborator is for you.