MathJax + MarkDown = MathDown.
As simple as that. The most minimalistic GitHub-flavoured MarkDown editor, with MathJax support with LaTeX/AsciiMath input, in a webbrowser.
Directly type in all the MarkDown. Enclose your AsciiMath with single dollars ($
),
and LaTeX with backticks ('`'). Try it live: https://shivaprsdv.github.io/mathdown/mathdown.html
Here are some webpages I created purely using Mathdown: