The static blog generator, Octopress, does not generate per category RSS feeds by default. I thought I would need a plugin to do this but it is quite easy and a plugin is overkill. All that you need to do is create a feed file with the appropriate filtering to limit the category.

To create a per category feed, copy the default feed source/atom.xml file to say source/emacs.xml. I updated the <title> value and the for post loop to only use the emacs categories. Here is my file:

&lt;?xml version="1.0" encoding="utf-8"?&gt;
&lt;feed xmlns="http://www.w3.org/2005/Atom"&gt;

  &lt;title&gt;{{ site.title | xml_escape }} - Emacs&lt;/title&gt;
  &lt;link href="{{ site.url }}/atom.xml" rel="self"/&gt;
  &lt;link href="{{ site.url }}/"/&gt;
  &lt;updated&gt;{{ site.time | date_to_xmlschema }}&lt;/updated&gt;
  &lt;id&gt;{{ site.url }}/&lt;/id&gt;
  &lt;author&gt;
    &lt;name&gt;{{ site.author | xml_escape }}&lt;/name&gt;
    {% if site.email %}
      &lt;email&gt;{{ site.email | xml_escape }}&lt;/email&gt;
    {% endif %}
  &lt;/author&gt;
  &lt;generator uri="http://octopress.org/"&gt;Octopress&lt;/generator&gt;

  {% for post in site.categories.emacs limit: 20 %}
  &lt;entry&gt;
    &lt;title&gt;{{ post.title | xml_escape }}&lt;/title&gt;
    &lt;link href="{{ site.url }}{{ post.url }}"/&gt;
    &lt;updated&gt;{{ post.date | date_to_xmlschema }}&lt;/updated&gt;
    &lt;id&gt;{{ site.url }}{{ post.id }}&lt;/id&gt;
    &lt;content type="html"&gt;{{ post.content | expand_urls: site.url | xml_escape }}&lt;/content&gt;
  &lt;/entry&gt;
  {% endfor %}
&lt;/feed&gt;