CommentPress is an open source theme for the WordPress blogging engine that allows readers to comment paragraph by paragraph in the margins of a text. Annotate, gloss, workshop, debate: with CommentPress you can do all of these things on a finer-grained level, turning a document into a conversation. It can be applied to a fixed document (paper/essay/book etc.) or to a running blog.
BuddyPress is a suite of WordPress plugins and themes which extends WordPress MU and brings social networking features to a new or existing installation.
This Plugin will transform WordPress into a custom knowledge Base application to power your documentation needs. You'll be able to add articles and frequently asked questions, rate content, show related articles, and much more!
Wikis, blogs and podcasts: a new generation of Web-based tools for virtual collaborative clinical practice and education BMC Medical Education 2006, 6:41
"I own the collection of comments on my blog, and you own the comments you've placed on my blog and all others. I should be able to back up a complete set of comments on my blog, and also back up a copy of all comments I've placed on all blogs."
kwout is a tool which allows you quote a part of a web page as an image with an image map. To use the service, add the bookmarklet to your browser (no sign up).