The Network News Transfer Protocol (NNTP) provides bulletin board services. The Usenet newsgroups are famous examples of globally-relayed bulletin boards (these global-newsgroups exist in the "cloud" without any individual home server, but this can sometimes lead to the loss of a "thread"). Server access requires using a NNTP News Reader client, or a Browser that understands the URI "news://". Just copy & paste the full NNTP address into your News Reader. Below are addresses to various publicly open NNTP servers.
[IANA Port assignment = 119]
Note: Unmoderated newsgroups can be posted to directly, but postings to moderated newsgroups must first pass through the newsgroups' moderator. Charters and FAQs for many of the moderated global-newsgroups, describing how to post and what is acceptable to post, can be found at this link
Be aware that global-newsgroups being offered are always at the discretion of the individual Relay Server maintainer.