Usetnet was (technically still is) essentially decentralized text-only reddit, with an open protocol and a client you can choose. You can post/read on a global network. The problem is that very few groups are still active and probably dying.
Back in the day ISPs would give you an email account, some static web space accessible via FTP and access to the local NNTP (usenet) server as standard, which is why it was popular. usenet servers were peered with each other, sharing a large global namespace (servers could have local-only groups too, but that's a detail).
At the beginning, most of the online discussions happened there.
As open-source development grew, the main issue was that creating and getting approval for a group was bureaucratic/complicated and slow. As this was global and automatically peered, there was also a "minimum" number of requests to be eligible. For this reason, small groups started to move to mailing lists instead which didn't require special approval and became the new de-facto standard.
For a long time, bi-directional nntpmailing list software was standard for large lists. nntp clients were always designed to work with huge amount of messages efficiently compared to mail clients. I was following hundreds of groups at the time, and I still consider nntp fantastic from the user perspective.
Spam and trolls were another problem with such a public global network. Policing was hard. This is just a very short summary (it ignores completely the problem of piracy/warez and the binary split..)