Haystack is a product for Plone used to do auto-classification of content. I've talked about it a little bit before but never given much of an introduction to it before.
Haystack is built around libots which is available for many platforms. ots is a set of Python bindings to the library and I've made it available on cheeseshop. This means you can ez_install its
or you can grab it yourself from either:
cheeseshop or from svn
After that you'll want to get Haystack, the product for Plone that will get you started.
Once that is installed you'll have access to a new portlet that will show you the interrelationships between content on the system and a tool that will give you more control over the analysis of content.
haystack_tool.summarize(unicode, asHTML=False, ...)
return either a unicode or html highlited summary of the text you passed in
haystack_tool.topics(unicode, count=5, ...)
return a list of topics extracted from the content
Its pretty simple to things like auto suggest keywords/subjects with this tool and Bling in conjunction. Topic maps and other fun things are pretty simple as well. As it gets more use there are many options to expand on the kind of classification and clustering that are available.