I just installed https://github.com/ypocat/gfms. It does a very good job rendering github flavored markdown. It detects changes in your markdown, so you just put your browser and editor side-by-side. It is Node.js, so it should work fine on any platform.
If you have Node.js is installed, the installation is simple:
sudo npm install -g gfmsgfms --port 9999 (in your project directory)http://localhost:9999/ (open with any browser)
