I don't think there is any real user-friendly app ready. But those are some prototypes/ideas:

- https://github.com/taviso/nntpit (reddit to nntp)

- https://gitlab.com/antekone/desugar (reddit/lobsters to nntp)

- https://github.com/nkizz/mop3 (mastodon to pop3)

- https://github.com/NattyNarwhal/LobstersNntp (lobste.rs to nntp)

(although reddit gateways probably stopped working after Reddit closed the doors to their API)