DAViCal CalDAV & CardDAV Server
DAViCal CalDAV Server (previously called the Really Simple CalDAV Store or RSCDS) is a project by Andrew McMillan to create a straightforward CalDAV server for shared groupware calendaring. The project is written in PHP and uses a PostgreSQL database for backend storage.
Visit the home page for DAViCal CalDAV Server for more detailed information about this project.
Getting the Code
Debian packages are available from here:
deb http://debian.mcmillan.net.nz/debian/ unstable awm
and here are DAViCal packages in other formats.
You'll need Andrew's Web Libraries too.
The fastest way to get help is on IRC. Join the #davical channel on irc.oftc.net and we'll see what we can do to get you going. The sourceforge site also has a mailing list and forums.