A single page indexing all the categories and posts

category_post_listing.mako

<%inherit file="_templates/site.mako" />

<% 
   # Generate a map of categories to posts
   category_post_map = {}
   for p in bf.posts:
       for c in p.categories:
           try:
               category_post_map[c.name].add(p)
           except KeyError:
               category_post_map[c.name] = set([p])
%>

<ul>
% for category, posts in category_post_map.items():
<li>${category}
  <ul>
    % for post in posts:
     <li><a href="${post.permalink}">${post.title}</a></li>
    % endfor
  </ul>
</li>
% endfor
</ul>