external-rss.rb

# http://stackoverflow.com/a/27850727/733677

require 'open-uri'
require 'rss'

module Jekyll

    # Runs during jekyll build
    class RssFeedCollector < Generator
       safe true
       priority :high
       def generate(site)

          rss_items = RSS::Parser.parse(open('https://blog.chartmogul.com/feed/').read, false)

          # Create a new on-the-fly Jekyll collection called "external_feed"
          jekyll_items = Jekyll::Collection.new(site, 'external_feed')
          site.collections['external_feed'] = jekyll_items

          # Add fake virtual documents to the collection
          rss_items.items.each do |item|
             title = item.title
             #content = item.description
             guid = item.guid
             path = "_rss/" + title + ".md"
             path = site.in_source_dir(path)
             doc = Jekyll::Document.new(path, { :site => site, :collection => jekyll_items })
             doc.data['title'] = title;
             #doc.data['feed_content'] = content;
             jekyll_items.docs << doc
          end
       end
    end

end

template.html

{% for item in site.collections['external_feed'].docs %}
    <h2>{{ item.title }}</h2>
{% endfor %}