ZWiki is a sehr-cool beast, as far as Wikis go. A very attractive feature, seen all over the
Zope.org web site is
Ken Manheimer's work on page/parenting relationships. This makes it so that Wiki pages, although stored in a flat namespace (all in one folder) can appear to be hierarchical, depending on which page generated which page (parenting can be altered of course). This in turn leads to cool things, like a structured table of contents (see the Zope 3 wiki's
TOC Here).
It's especially cool in that it's fairly easy to change the hierarchical structure of the Wiki - by looking at a page's backlinks, one can reparent a page to one or more of its linkers. Essentially, new logical structures can grow independent of the physical structure.
I've used a similar feature in a recent simple content system, wherein all documents were stored in a single folder, but the users entering content could classify documents in one or more categories. The main pages on the site were basically database queries (actually, catalog queries) based on the classifications. Thus, the site was built out of a simple logical structure rather than a physical one, which allowed documents to appear in more than one place if they needed to be. It's no unique concept, "Radio" and some other blogging tools allow this, much to my delight.
In the simple compound system I did for that customer, the flat namespace also allowed simple inter-document link management. The author could say "document A links to document B", and when document B was deleted, the link to it would also evaporate. For some reason, doing deep inter-object linking in "Zope" is still tricky business, but there's hope on the "Zope 3" horizon (some of which looks like it may be backported to Zope 2).