Part of the website for the recent OSCOM3 (Open Source Content Management) conference is a terrific listing of Open Source content management systems and frameworks, a 1-2 sentence description of each product and a link to the product’s homepage.
Even more useful, though is the Feature Comparator. This tool allows you to build your own hierarchical directory based on facets of your choosing.

For example, at DMOZ under Content Management, there are folders for PHP and Perl and Python. This is the programming language facet (or property or attribute) and it has three possible values.
 
Suppose you wanted to view CMS by web server (Apache, IIS, etc.) first, and then by CMS Framework (Cocoon, Midgard, etc.) and only then by programming language?
 
With standard taxonomy technology, you are out of luck. Here you can select the facet you want at the top of the hierarchy, then another facet for the next layer in the hierarchy, etc.

And when you are done, you can save your hierarchy as an OPML file. Nice widget. Codes’s all there, too…