In migrating to Discourse, we had a pre-existing discussion platform on NNTP. To keep the two working side-by-side, I wrote a small plugin that syncs them!
NNTP newsgroups get assigned to pre-existing Discourse categories. Posts from Discourse go to NNTP, and posts from NNTP go to Discourse.
It also attempts to match email addresses with existing Discourse users, so as long as you have your NNTP users in Discourse, posts synced from NNTP look identical to any other discourse-created post.
There are some limitations, such as support for cross-posting and canceled messages, however in my testing this covers 95% of our use.
Contributions & feedback welcome! GitHub · Where software is built