One of the goals of the CalDAV integration with Sakai is to test simultaneously against at least two CalDAV server implementations. If we call upon our network of volunteers, we may be able to test with more systems by the time we're finished. We're using Zimbra because that's the system Georgia Tech is rolling out, and Bedework because it's a free (as in beer and freedom) system that many in our community may be interested in trying.
The advantage of testing against more than one system from the get-go is that hopefully we will avoid building in any idiosyncrasies that arise from one particular server implementation.
I have Zimbra running on a Dell workstation from 2000 that was a "tower of power" in its day. Yesterday I took delivery of an Asus eee PC 701, a two pound notebook with at least the horsepower of the old Dell.
For the curious, here's how easy it is to get a demo of Bedework up and running. The first line will depend on your system, but this is how it works on my teeny tiny eee PC. :-D
The database log will tie up that terminal window, so open another one.
That's it. You access the system by opening http://<servername>:8080/bedework in a browser.