Github Markdown Server
Use your favorite editor to edit a markdown file, Run the server and open the file. Saving in your editor updates instantly in the browser.
gem install github-markdown-server
This will start a server serving in the current directory and all child directories and open a browser (on a mac) showing README.md converted to html. If you navigate to a directory name only child directories and .md files are shown in a directory listing. If there is a README.md file in that directory it will be appended to the directory listing.
If you are deep down inside a git repository and you want to serve the whole repository (so that relative links will work) then this command will do that for you.
github-markdown-server -d $(git rev-parse --show-toplevel) somefile.md
There is a contrib directory with an emacs lisp file which will start a server and open a file for you. It'll keep track of which servers it has started and reuse an existing server if a file you want to preview is under that server's serving directory.
Please feel free to send me pull requests! This is my first Ruby project and it always feels like my first time when I write Emacs Lisp.