FeedFinder is a project mainly written in Ruby, it's free.
Discovers feeds for a given URL
This simple script takes a URL and returns all feeds found at that address.
FeedFinder.feeds('http://www.example.com')
=> Returns an array of all found feeds (and an empty one if none are found).
FeedFinder.feed?('http://www.example.com')
=> Whether or not the URL is a feed