Calendar Server

I have been searching far and wide for a decent cross-platform calendar server that’s CalDAV compatible. We use Groupwise at work, which is great for Windows clients.  Anyone who’s used the Mac and Linux client knows that it’s just not a good experience.  There are several features offered in the Windows client that are lacking in OS X and Linux.  Does anyone else find that odd considering Groupwise is a Novell product?  There IS the SOAP port possibility, but the Groupwise admins refuse to open it for reasons I’m not aware of.

Anyway, Here’s a few I’ve found:
  1. Darwin Calendar Server – this is the same exact (actually newer) server as what Apple offers on OS X Leopard Server, sans the GUI.  It’s python based, and the Wiki contains the basic stuff you need to know to get it up and running.
  2. Cosmo Calendar Server – part of the Chandler project.  It’s java based, and looks promising.  Last I looked into it, it was very early alpha.  It seems to have made a bit of progress since then.  Now it seems to offer an all around solution:  a client and server, as well as a free (for now) hosted server called Chandler Hub.
  3. Bedework - a calendar server also built on java with CalDAV support.  We tried setting this up in our offices once, but Tomcat kept crashing.  I might try again from source.
  4. DAViCal – another CalDAV server.  I haven’t tried it out because I’m not very proficient with PostgreSQL.
  5. Zimbra – A bit overkill for someone looking for just a calendar server, but it’ll get the job done with a web interface and CalDAV support.
  1. OS X 10.5 Server – Much more than a calendar server, but it’ll get the job done.  Basically gives you a GUI to Darwin Calendar Server, I think.
  2. Nighthawk – One of my top choices for a commercial calendar server and client.  It’s not available yet, but from what I’ve seen it will be fantastic.
In a perfect world, everyone would use iCal so I could deploy BusySync, which I use myself for my personal calendar and is nothing short of phenomenal.  It’s great for LAN calendar sharing, as well as it’s ability to tie into Google Calendar.
I considered using Google Calendar as a calendar server for my group at work, but the fact that it was not internal to our organization doesn’t sit well with me.
If you know of anything I haven’t listed here (not Exchange!!), please let me know!