Ruby equivalent of Sphinx documentation generator?
Another couple of options would be to use Middleman which is a static site generator that accepts either Kramdown or Markdown as input.  
There are also frameworks that are designed specifically for technical documentation that use Middleman (both of which are on GitHub) including lord/slate and pnerger/dpslate (the later is a fork of the former and provides some enhancements that were not appropriate for pulling).  The Slate format provides a format for documentation that includes many of the features of Sphinx with some additional enhancements.  It features a three-pane view of a document which includes an automatically generated Table of Contents, a Main center body, and then sample code panel to the right.  Like Sphinx the sample code has syntax highlighting.
Ruby has a few good document generators like Yard, rDoc, even Glyph.  The thing is that Sphinx does websites, PDF's, epub, LaTex...etc.  It does all these things in restructuredtext.  
Is there an alternative to this in the Ruby world?  Maybe a combination of programs?  If I could use Markdown as well that would be even better.