Free / Opensource Appointments Application ?

http://www.mozilla.org/projects/calendar…
Welcome to the Calendar Project. This is the home of
* the Sunbird calendar application
* the Lightning integrated calendar and
* the Calendar extension
We are striving to build cross-platform fully standards-based calendar client applications based on the open iCal standard.
Sunbird vs. Lightning vs. Calendar Extension
* Sunbird is our standalone calendar application. It doesn’t need another client application to run at the cost of a larger download and higher memory requirements. Because of its standalone nature, Sunbird does not offer any kind of tight integration with an e-mail application, such as Mozilla Thunderbird.
* Lightning is a calendar extension for Mozilla Thunderbird. It offers calendaring features directly in the Thunderbird User Interface. Further integration features, such as e-mail invites or addressbook integration are planned for future releases.
* The Calendar Extension is the old calendar extension for Mozilla Thunderbird and Mozilla Firefox. It offers some of the calendaring features of Sunbird and Lightning, but lacks the tight integration of Lightning into the e-mail application.
Due to resource constraints, the Calendar extension has been discontinued. Further development work will focus on Sunbird and Lightning entirely.
Latest News
The Calendar Project development team keeps a development weblog. It is intended for everyone who is looking for in-depth, up-to-date information about current events in development.
Wednesday, August 2nd, 2006:
John T. Haller has just released Sunbird 0.3 alpha2 in a portable edition. Head over to his site to check out Mozilla Sunbird – Portable Edition, if you would like to carry around your personal copy of Sunbird everywhere.
Thursday, May 11th, 2006:
The Sunbird team is proud to announce the completion of Sunbird 0.3 alpha2 for Windows, Linux and Mac OS X. This is a major milestone on the road to the final Sunbird 0.3 release. Thanks go to all developers, testers and other supporters of the project.
Detailed release notes (about improvements, bugs, etc) can be found at the Sunbird 0.3 alpha2 release notes page.
We would like to emphasize the fact that while Sunbird 0.3 alpha2 has seen lots of improvements over Sunbird 0.3 alpha1, we do not consider it to be a production-quality release. It is pre-release software and should be treated as such. This means that this release may contain serious bugs leading to application crashes, dataloss or other unforeseen consequences.
You can find builds for the different platforms on our download page.
Localized builds are also available.
Sunbird™ and the Sunbird logo are trademarks of the Mozilla Foundation. All rights reserved.