It's a simple COM-.NET plug-in created for Outlook 2003. Once installed, every Outlook user will be able to subscribe, delete and reload a remote iCalendar.
Citadel is a turnkey open-source solution for email and collaboration. One simple installation delivers a multitude of powerful features, including: email, calendaring/scheduling, address books, bulletin boards, mailing list server, instant messaging, multiple domain support, modern AJAX-style web interface
Hula is a calendar and mail server whose goal is to be fun and easy to use, while scaling effortlessly from small groups to large organizations with thousands of members. Hula is an open source project led by Novell (http://www.novell.com).
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Open Source Collaboration, providing:
* Integration with your existing Linux mailserver
* Native mobile phone support
* Outlook "Look & Feel" webaccess
* Stable Outlook sharing (100% MAPI)
Zimbra is an open source server and client technology for next-generation messaging and collaboration. Zimbra delivers innovation for both the administrator and the end-user as well as compatibility with existing infrastructure and applications (both open source and proprietary).