From the README:

newsfish, quite simply, is a batch USENET news reader. In other words,
it is not interactive, and it has a very simple user interface. The power
of newsfish is that it can sift through articles and save only the ones
that match your criteria. It does this by applying a set of regular
expressions (a la grep/egrep) to the headers of each article.

Articles are saved in mailbox format, which makes them suitable for
viewing under most popular mail readers.