Almost every existing md to PDF goes through LaTeX: kramdown, pandoc, multimarkdown, etc.
So far I have only found:
Gimli, but it does not seem very active (last commit 7 months ago). Backend?
markdown_prawn. Not many stars. Last commit 3 years ago.
Kramdown Prawn experimental converter. Experimental.
If you can convert the HTML subset generated from Markdown to PDF well, then that is a solution, but I am yet to find a software that does it properly. For example, PhantomJS conversions break markdown links
<http://a.com>, which show as simple styled text on the PDF, not as clickable links that open on preferred browser, which are generated through LaTeX conversions.
O'Reilly Atlas is doing it for their HTMLBook (HTML5 subset), but they're not gonna open source that anytime soon.
Related: Ruby only SO question.
Why I want this: LaTeX is slow, produces horrible error messages, is hard to install, and is overly complex for the small subset needed for Markdown.