This bookmarklet gives you a code editor in your browser with a single click.

notepad.html

data:text/html, <style type="text/css">.e{position:absolute;top:0;right:0;bottom:0;left:0;} .e *{font-size:14px;}</style><div class="e" id="editor"></div><script src="http://d1n0x3qji82z53.cloudfront.net/src-min-noconflict/ace.js" type="text/javascript" charset="utf-8"></script><script>var e=ace.edit("editor");e.setTheme("ace/theme/monokai");e.getSession().setMode("ace/mode/ruby");</script>
<!-- 
For other language: Instead of  `ace/mode/ruby`, Use

Markdown -> `ace/mode/markdown`
Python -> `ace/mode/python`
C/C++ -> `ace/mode/c_cpp`
Javscript -> `ace/mode/javascript`
Java -> `ace/mode/java`
Scala- -> `ace/mode/scala`
CoffeeScript -> `ace/mode/coffee`
and 
css, html, php, latex, 
tex, sh, sql, lua, clojure, dart, typescript, go, groovy, json, jsp, less, lisp, 
lucene, perl, powershell, scss, textile, xml, yaml, xquery, liquid, diff and many more...




For other theme: Instead of  `ace/theme/monokai`, Use

Eclipse -> ace/theme/eclipse
GitHub -> ace/theme/github
TextMate -> ace/theme/textmate
and 
ambiance, dawn, chaos, chrome, dreamweaver, xcode, vibrant_ink, solarized_dark, solarized_light, tomorrow, tomorrow_night, tomorrow_night_blue, 
twilight, tomorrow_night_eighties, pastel_on_dark and many more..
-->


<!-- If you want a markdown converter use this : !-->
data:text/html,<style type="text/css">.e{position:absolute;top:0;right:50%;bottom:0;left:0;} .e *{font-size:14px;} .c{position:absolute;overflow:auto;top:0;right:0;bottom:0;left:50%;}</style><div class="e" id="editor"></div><div class="c"></div><script src="http://d1n0x3qji82z53.cloudfront.net/src-min-noconflict/ace.js" type="text/javascript" charset="utf-8"></script><script src="http://cdnjs.cloudflare.com/ajax/libs/showdown/0.3.1/showdown.min.js"></script><script> function showResult(e){consoleEl.innerHTML=e}var e=ace.edit("editor");e.setTheme("ace/theme/monokai");e.getSession().setMode("ace/mode/markdown");var consoleEl=document.getElementsByClassName("c")[0];var converter=new Showdown.converter;e.commands.addCommand({name:"markdown",bindKey:{win:"Ctrl-M",mac:"Command-M"},exec:function(t){var n=e.getSession().getMode().$id;if(n=="ace/mode/markdown"){showResult(converter.makeHtml(t.getValue()))}},readOnly:true})</script>
<!-- Press Ctrl+M or Command+M to convert your markdown code to html :) -->