I posted to delicious.com

Open-source collaboration platforms

http://wordflex.wordgym.com/open-source_collaboration.html

Cyn.in, which is a beautifully designed solution that suffers from the complexity of its underlying architecture (it's based on Plone, which in turn is based on Zope... the result is a system that is gorgeous to look at, but achingly slow to use on anything but a very powerful server. If you've got one of those, however, you really ought to take a look -- Cyn.in takes the desktop connection thing to a glorious extreme!).