Usenet has some interesting differences from what we’re using now:

Clients and servers:

• There is no default UI. Everyone is using client software of their choice.
• Your client software — not the server — is responsible for keeping track of which newsgroups you’re subscribed to, and which messages you’ve read in those groups.
• Posts are copied from server to server based on whether the receiving server is configured to accept posts in a particular newsgroup (or collection of newsgroups).
• Posts are not retained forever, except by archive services like Deja News (later Google Groups). Servers automatically expire posts to save disk space. Expiration can be tuned; a server might keep sci.math posts forever, but expire alt.binaries.* posts in a day because binaries (i.e. images and other non-text media) are large.
• Server peering relationships are arranged by the server admins; there’s no default open federation.
• If a server goes offline for a while, it can reconnect to its peers and pick up posts that it missed. But because of expiration, it might have just missed some posts forever.

Newsgroups:

• Newsgroups look like containers-of-posts in the UI, but are actually implemented as topic tags in post headers.
• A newsgroup identity is global, unlike a Lemmy community. A newsgroup doesn’t have a home server.
• A single post can be in multiple newsgroups without duplication. This is the original meaning of “crossposting”. (Reposting the same message to different groups is “multiposting”.)

Newsgroup management:

• Newsgroups are arranged in hierarchies. Some of these are global (e.g. sci.* or alt.*) while others are regional (like ne.* for New England) and were originally unlikely to be carried outside of a geographical region.
• New newsgroups in most global hierarchies are created through a formal discussion and voting process, intended to ensure that a new group is well-placed and has an audience.
• In the original moderation system, you post to moderated groups by emailing your post to the moderator, who posts it for you.
• This was largely replaced by “retromoderation” which is what we think of moderation today: anyone can post, but the moderator is allowed to cancel bad posts. The first modbot was invented for Usenet.
• Federated deletion is handled through “cancel messages”. Supposedly, only the author, moderator, or a server admin were supposed to be able to cancel a message. However, forged cancels were a common problem.

Threading:

• There is no post/comment distinction; they’re all just messages, commonly called posts. A post can be marked as a reply to another post; a new thread is started by a post that is not a reply to any other post.
• Clients typically present posts in a threaded tree structure, but the server doesn’t need to know about threads, just posts. Threading is a client-side feature; the server just gives your client the posts, and your client constructs the threaded view by following references in post headers.
• Because newsgroups and threading are independent, a single thread can actually span multiple newsgroups! A conversation can start in comp.lang.lisp, then someone mentions their cat, then a reply crossposts to rec.pets.cats, a later reply drops comp.lang.lisp and now it’s a cat thread. This is either pleasingly organic or really annoying depending on your attitude.

I loved the Zones of Thought books. I wish Vernor Vinge would write more.