eruby (sorry for the extra E) interprets a RubyLanguage code embedded text file. For example, eruby enables you to embed a Ruby code to a HTML file.
http://raa.ruby-lang.org/project/eruby/
It's just the usual template system:
<% if boolean_value %>
<em><%= ruby_string %></em>
<% end %>
Wanted: A version of HtmlTidy that skips over these instead of freaking out.
See also MongrelEeRuby.