I do not have trouble with building the course structure. I've got a problem trying to puzzle out the way they incorporated similar or any other groups much like confirmed one. For instance, when you purchase the "computer systems / software" category you will notice a category for consumer information, games, sports, home etc. These groups don't belong directly underneath the software category, yet they're similar.

How does one implement something similar to this?

In the FAQ page on DMOZ (http://world wide web.dmoz.org/help/geninfo.html#search) :

The ODP is really a Web directory, not really a internet search engine. Although we provide a search query, the objective of the ODP would be to list and classify web sites.

Based on their FAQ their submissions are handled through the users list, and I'd take that to incorporate every aspect of the content and it is associations, similar to Wikipedia.

Nevertheless, I do not think they are creating associations between content groups that's offered dynamically. I believe they're managing a Cms and also the category associations are merely area of the content.