MacDown is an open source Markdown editor for OS X, released under the MIT License. It is heavily influenced by Chen Luo's Mou.
Ranked in these QuestionsQuestion Ranking
Pro Free and open source
Pro Real-time split-screen preview
MacDown's main view is split into two panels. The user types on the left and the Markdown is rendered on the fly in the right panel. This helps users to better understand the way they are formatting their document.
Pro Good auto-completion
MacDown has a good built-in auto-completion engine for Markdown symbols.
Pro Markdown previews can be customized with CSS
You can use a CSS file to customize the rendered output and the file preview you are working on will display the rendered Markdown with the custom CSS styling on top.
Pro Supports syntax highlighting in fenced code blocks
MacDown has syntax highlighting support for various languages when writing code in fenced code blocks.
Pro Support for GFM
Pro Ideal for day-to-day programmers' work and MarkDown novices alike
Using MacDown for the notorious README.md use case gets you going without reading any manual or requiring any configuration values. Think of it as a sort of TextEdit for MarkDown files. Thus its shortcomings - neither powerful nor versatile - turn out to be a PRO for novices trying to jump on the MarkDown bandwagon. Open its help and you'll immediately find yourself editing the MacDown's MarkDown help file, a MarkDown primer with some MacDown menus and configuration added.
Con Not very versatile
MacDown is not very powerful or versatile. It's not customizable or extendable. This is what makes it so simple, but it's not for people who want more from their tools.
Con The Markdown preview is rather heavy on the CPU
The Markdown preview needs a lot of resources to keep rendering on-the-fly after each keystroke. A single keystroke in the editor panel may trigger up to 5 seconds of max-CPU usage.