Bedework is an open-source calendar system, built with an emphasis on higher education. It conforms to current calendaring standards, which means you can share events with iCal, Outlook or Google calendars.
It wil run as a portlet in UPortal, JetSpeed2, BEA and Liferay.
It's used by a wide variety of schools such as Brown, Yale, Julliard, University of Chicago and Illinois State University.
The very useful web site clearly communicates everything you need to know about Bedework, an obvious indication of how well-thought out the product is.