Marked.js - A full-featured markdown parser and compiler, written in JavaScript. Built for speed.
NotePlan - Make plans inside an individual markdown note for every day in your calendar. Use it as a journal for your daily tasks and plan todos in advance. For Mac, iPhone and iPad.
Markdeep - Advanced Markdown renderer for the browser with full diagram support
markdown to web - Convert markdown to online web page
ShowdownJS - A Markdown to HTML converter written in JavaScript
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.