Hi -
I've done a lot of work with the FileNet document/content management system ... but it isn't exactly "Open source" ;-)
Two strong suggestions (both of which I've used and can vouch for .. if not in exactly this contect):
* Gallery2
<= It's easy to use, powerful ... and it might just give you everything you're looking for:
http://www.gallery2.org/
* MediaWiki:
http://www.mediawiki.org/wiki/Download
<= If you wind up going with MediaWiki, here's a book recommendation:
"Professional Wikis", Mark S. Choate, ISBN: 978-0-470-12690-5
You've got lots of other choices ... but these are the first two I'd suggest looking at.
'Hope that helps .. PSM