The Open Source Applications Foundation are developing Cosmo, which is a CalDAV server written in Java and Chandler, which is a CalDAV capable mail and calendaring application written in Python.
Basic setup is as follows:
Chandler describes itself as 'an experimentally usable calendar', and it certainly feels that way. It also will only synchronise to the CalDAV server either when you press the "Sync" button or with a default frequency of quarter-hourly. This is quite different to the other clients I have used which all aggressively push new and changed items to the server as soon as possible, but which may be lazy about fetching updates.
Operation with DAViCal seems generally fine although Chandler does not correctly display the account information correctly, even if it seems to remember it internally.