User script to Markdownify text in ADN Alpha. Oddly, I seem to have to launch it and hit Run to have it actually run on the page just now. :\

markdownify-alpha.js

// ==UserScript==
// @id             com.jeremywsherman.adn-alpha-markdown
// @name           Styled Markdown Text for ADN Alpha
// @version        1.0
// @namespace      com.jeremywsherman
// @author         Jeremy W. Sherman
// @description    Recognizes and fontifies **bold**, *italics*, and `code` in ADN posts.
// @include        https://alpha.app.net/
// @run-at         document-end
// @grant          GM_xpath
// ==/UserScript==

// Inspired by: https://alpha.app.net/remus/post/19801955

var post_nodes = function () {
  //console.log('post nodes')
  var result = document.evaluate(
    "//span[contains(@class, 'post-content')]", document, null/*nsResolver*/,
     XPathResult.ANY_TYPE, null/*result*/);

  var nodes = [], node = null;
  while ((node = result.iterateNext())) {
      nodes.push(node);
  }
  return nodes;
}

var markdownify = function (text) {
  //console.log('markdownify', text)
  bolded = text.replace(/\*\*([^*]+)\*\*/g, '<strong>$1</strong>');
  italicized = bolded.replace(/\*([^*]+)\*/g, '<em>$1</em>');
  coded = italicized.replace(/`([^`]+)`/g, '<tt>$1</tt>');
  return coded;
}

var nodes = post_nodes();
var i = 0, e = nodes.length;
console.log('found ', e, ' posts')
for (; i < e; ++i) {
  var html = nodes[i].innerHTML;
  var marked_up = markdownify(html);
  nodes[i].innerHTML = coded;
}