StackEdit is a full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
MarkdownPad Markdown editor for Windows.
Markdown, Please! is a service that instantly converts websites into Markdown.
CommonMark.org has a great interactive tutorial on Markdown.
Code segments could be rendered by specifying language name. For example, using Pygments you could use the short names after the three ticks to render the code in that language syntax. You may look at a list of lexers to find the short names.
What is Markdown, and why is it better for my To-Do Lists and Notes? from Lifehacker dated 09/14/2012
Using Markdown in Quip is a how beautifully Quip uses Markdown in its application.
Why markup (and Markdown) matter a great article from the writer’s perspective.
It (HTML) is a great tool for publishing, but a less-than-perfect one for authoring.
5 Sites and Apps for Quickly Learning Markdown
Writing for the web with Microsoft Word is like commuting to work in an 18-wheeler.
Markdown Parsers help you parse the Markdown files and render the output in a browser friendly format (HTML).
Markdown Parsers are available in various programming languages: