Looking for the right "links portal" software

[pom]

What dynamnic open-source content management system(s) would you look
at to meet the following specific situation?

- The requirement is for a large institutional client who wishes to
build a public portal consisting of annotated links to external
materials in a particular subject area.

- Links on the site will be to materials on separate servers offered
through sites of organizations within the institution. There are maybe
2-3000 sites and docuemnts to be linked.

- The central manager of site should be able to categorize (tag)
linked sites using set of defined (meta) characteristics, and add
annotations

- The central manager of site should also be able to create and update
links, manage site menu structure, using browser, without html skills

- Links should be searchable by users using combinations of metatag
keywords

- Eventually, other authors within the organization should be
permitted to create and update linked materials (owned by their
internal organization.)

- The resulting pages and links lists viewed by users must be W3C
compliant, and meet institutional look and feel requirements.

My question is what proven "off-the-shelf" open source software
products (including already-developed proprietary products) come
closest to meeting these specific requirements, such that a minimum of
custom programming would be create this portal?

Any advice and pointers to candidate products would be most
appreciated.

- P