A list of Calendar Sharing Applications
From a forum post by Patrick Shaw.
http://www.officecalendar.com/
http://www.ical.net/ (this is a listing of other calendar tools)
http://www.meetingmaker.com/products/meetingmaker/free_trial.cfm?source=ov_cal3free1
Contributors:
Patrick Shaw (author)
Zac Mutrux (reposted as book)

OpenExhibitionist: Open Source Calendar & Curating Web App
We're about to launch a new Open Source Web application, OpenExhibitionist, publicly. It will be available both as a (free) download or on a (free) subscription/account basis. Initial funding came from the Irvine Foundation via the 9th Street Independent Film Center in San Francisco. We are actively seeking further funding as well.
For now it is a (PHP/MySQL) "Resource Management" tool based on the iCal standard that allows an organization to schedule and inventory assets (resources), e.g. for an equipment facility (like Film Arts Foundation in San Francisco) to rent out rooms and gear, and have schedules posted online. Consituents can subscribe to or download calendars, get RSS feeds, or look up information in real time.
V.2x will have support for more content management and curating tools, for example there will be functionality for a film festival to track a movie through the process of submission to screening.
It will be available for download via SourceForge in a few weeks (probably around Aug 15, 2005).