Podcast is a simple library and command line utility for creating
podcast files from a directory of mp3 files. Podcast will 
examine mp3s, extract metadata from ID3 tags, and build an RSS
file which can then be podcast clients to download the mp3s.

You'll need to install the Ruby mp3info library installed before podcast
will work:

    gem install ruby-mp3info

Or you can grab ruby-mp3info here:

    http://rubyforge.org/projects/ruby-mp3info/

Once you've installed ruby-mp3info and podcast you should have a 
command line utility you can run on a directory of mp3 files:

    % podcast --dir=/home/ed/mp3s --out=podcast.rss

Please note:
This used to be hosted at http://podcast.rubyforge.org/
However, that version no longer works with newer versions of Ruby.

I have made changes so it to works and after getting no answer from the author or via the list on rubyforge have decided to upload my version to https://github.com/boncey/ruby-podcast