A Jekyll plugin that provides an Rmarkdown "converter," so you can write your posts and pages in RMarkdown and save them in your site's _drafts or _posts directory with the extension Rmd or Rmarkdown.
To install, simply save rmarkdown_converter.rb in your jekyll _plugins directory. You'll also need to install rinruby, probably from RubyGems:
gem install rinruby
This code borrows heavily from the sample converter on the Jekyll plugins documentation page and this post by Simon Elliston Ball.
Now has its own repository.