What powers this page?

All the JavaScript you need (you don't have to host anything, let the YUI CDN do that):

<script type="text/javascript" src="http://yui.yahooapis.com/3.5.1/build/yui/yui-min.js"></script>
<script type="text/javascript">
YUI().use('gallery-markdown', function(Y) {
    output.setHTML( Y.Markdown.toHTML("# This is your markdown\n\nThis is your gun.") );
});
</script>
       

Here's the actual code powering this page