I would like recommendations for faceted browsing systems that include
authentication, and easily support multimedia content and metadata.  The
ability to add comments and tags to content, and browse by tag cloud is
also desirable.

My skills include ColdFusion, PHP, CakePHP, and XML/XSL.  The only
system I've worked with that includes faceted browsing is XTF, and I
don't think it's well suited to this.  I am willing to learn a new
language/technology if there is a system that includes most of what I'm
looking for.

Please let me know of any open-source systems you know of that might be
suited to this.  If you have time and interest, see the detailed
description of the system below.

Thank you,
Jill Earles

Detailed description:

I am planning to build a system to manage a collection of multimedia
artwork, to include audio, video, images, and text along with
accompanying metadata.  The system should allow for uploading the
content and entering metadata, and discovery of content via searching
and faceted browsing.  Ideally it will also include a couple of ways of
visually representing the relationships between items (for example, a
video and the images and audio files that are included in the video, and
notes about the creative process).  The views we've conceived of at this
point include a "flow" view that shows relationships with arrows between
them (showing chronology or this begat that relationship), and a
"constellation" view that shows all of the related items, with or
without lines between them.  

It needs to have security built in so that only contributing members can
search and browse the contributions by default.  Ideally, there would be
an approval process so that a contributor could propose making a work
public, and if all contributors involved in the work (including any
components of the work, i.e. the images and audio files included in the
video) give their approval, the work would be made public.  The public
site would also have faceted browsing, searching by all metadata that we
make public, and possibly tag clouds, and the ability to add tags and
comments about the work.