discourse/app/views/categories/index.html.erb

<% @list.categories.each do |c| %>
  <div class="category">
    <h2><a href="/category/<%= c.slug.blank? ? c.id : c.slug %>"><%= c.name %></a></h2>
    <div class="topic-list">
      <%- if c.displayable_topics.present? %>
        <% c.displayable_topics.each do |t| %>
          <a href="<%= t.relative_url %>"><%= t.title %></a> <span title='<%= t 'posts' %>'>(<%= t.posts_count %>)</span><br/>
        <% end %>
      <%- end %>
    </div>
  </div>
<% end %>

<p><%= t 'powered_by_html' %></p>