There was a Haml-like language called GHRML a while back, but it seems to have disappeared. There is something like it called SHPAML: http://shpaml.webfactional.com/

Though I think Ruby has better markup libraries in general. For example, they have Nokogiri, which is an absolute joy to use for XML parsing. And implementations of Markdown and Textile with actual parsers, whereas Python Markdown and Python Textile are straight regex-using ports of the Perl/PHP versions. It's kinda sad really.