I have been incredibly pleased working with the Chandler project’s calendar server. It’s so easy to set up and get running if you let the documentation guide you through it. It would take you 30 mins, assuming you already have some basic linux and mysql knowledge.
My only gripe is that it won’t authenticate against directory services, such as OpenLDAP or Active Directory. I had a chat with one of the developers on IRC about this, and it didn’t seem like that feature would be added anytime soon. So, this would be a good way to share calendars for a smaller workgroup or at home.