Plans, the best web calendar.
Users say:
In my searches for a web-based calendar solution, Plans came out as the best of breed. It has a great user-interface and features that make it easy for my users to administer. Unlike most other web calendars, it properly displays multi-day activities.

For Admins/Webmasters:

For Users:

* The custom color select doesn't work in Safari, Opera or Konqueror.