podcatchd is a surpassingly simple podcatcher written in POSIX sh. Unlike some
non-GUI podcatchers, it's not a one-shot program you need to run from cron to
truly follow a podcast; you simply leave it running on a server (either in a
tmux/screen session or as a background daemon) and it slurps up podcasts as it
sees them. Also unlike most podcatchers, it is itself less than 200 lines of
code; the heavy work of parsing rss is done by the excellent rsstail tool
(https://github.com/folkertvanheusden/rsstail - you currently need to build
from git, for RSS enclosure support).

At the time of writing any POSIX-compliant system with a sane (and sufficiently
new) rsstail and curl installed should run podcatchd (though dash's trap
handling appears to be buggy). Other HTTP-fetching tools can trivially
substitute for curl, but rsstail already depends on libcurl to fetch RSS feeds.

For further usage information, see podcatchd.1 - markdown rendering online:
https://github.com/oldlaptop/podcatchd/wiki/podcatchd.1