Imagine a federated Reddit with extremely lax (or no) moderation, and files. Access to a Usenet server gives you access to an almost unlimited number of communities discussing almost any topic you can think of, some topics you've never heard of, some topics you don't want to be involved with, and (depending on which server you subscribe to) downloadable files.

I haven't used one in years, so I have no idea how accurate the previous paragraph still is.