"The list of features is a mile long but let me summarize them all down to this simple statement: everything just fucking works exactly as you would expect it to."
No, this is not about Debian Etch :-) (but I guess we could make that happen).
Here is the origin.
Sorry for indirectly advertising non-free software, I just liked the quote.
Martin, it seems (just at first glance) that Zimbra is licensed under a MPL license and is non-free:
"The Zimbra Collaboration Suite (ZCS) Server and Zimbra Ajax Toolkit are both licensed under the terms of the Mozilla Public License (MPL), and require that modifications made to existing files be given back to the Community."