Feed Me is a simple parser for RSS2 and Atom feed, adding other feed formats should be trivial. Feed Me is pretty minimal and basically only does translation/cleanup from different feed formats to a consistent API. It is designed to be minimal.
Feed Me is built on the excellent Nokogiri parser.
Use it like this:
file = File.read('some_feed.atom')
feed = .(file)
feed.entries.each do |entry|
Check out the specs or lib/feed_me/consts.rb for the complete API.
DISCLAIMER: This is very much alpha software, use at your own risk!