Due to the issue below, TextMate2 isn’t a good option anymore (I kind of like it and will keep on using it for general purpose text editing).
So any other great alternatives on the Mac for MD-files?
(and If the answer is Emacs or Vim, I’m not listening :-))
Macdown is open source and free. I have not personally used it, but a power-user of Markdown editors on OSX recommended it to me recently.
Atom has a couple of plugin packages you can use for Markdown editing.
Personally I like Atom and MultiMarkdown Composer, but here’s a snippet from an internal list we keep at my company to let people try and choose their markdown editor.
FYI including online ones too:
###Mac Markdown Editors
###Online Markdown Editors
(Updated to include Macdown which is kind of a replacement for Mou, the dev for which has ceased apparently)
Also, Marked. It’s a previewer, not an editor, but might be good in combination with an editor. It updates on save.
Macdown looks nice, but … with Hugo I do not need/want Markdown rendering when I get the real deal with Livereload.
I personally use Atom and put up with the slow opening speed. In most other ways it’s great and incredible extensible/customisable.
Sublime Text also has a free Beta at the moment and it’s a great editor, super fast, customisable and capable.
I personally use Sublime Text with the Markdown Editing which has a pretty clean theme, especially if you use the distraction free mode.
Atom and other editors should have similar packages.
Mou text editor is great and cheap. http://25.io/mou/
Has side by side and simple functions.
I forgot to mention that Atom also has Markdown preview installed by default and you can add Markdown Writer which gives a nice set of additional features - particularly helpful for code highlighting with fenced code blocks
I created a post about working with hugo in visual studio code.
Using VS Code here, coming from Sublime via Atom, and I’m not looking back. hugo server -w is doing great in conjunction with Code’s autosave mode, Code is by way faster than Atom, at least on a windows 8.1 machine here in the studio. Too lazy to test on Linux or Mac, but it’s available 
@boris I might give it a try. The CJK wrapping looks like a good feature, which I need.
I’m late on the thread, but nobody mentioned the apps I’m using.
Currently I’m writing my articles on iA Writer. It’s good looking, minimalistic editor that syncs between MBP, iPad and iPhone. Also, it makes text larger depending on the window size (no that’s not taken for granted on other apps). It helps on shaky trains.
If you ever write something big in .md files, check out Editorial. It has automatic contents table (dropdown on the interface) to jump between headings. Without it, it would be very difficult to find way.
Previously there were more differences, but new releases equalised both.
If you don’t want live rendering, then Sublime is great with lightweight plugins like MarkdownLight: https://packagecontrol.io/packages/MarkdownLight
I can’t recommend Sublime enough if you’re thinking about playing with a new editor. Well, maybe you’ve already spent years with it. It’s very powerful and snappy. Atom was killing me with its slowness. It’s so confusing that they would build a desktop text editor out of “the web”. Sometimes the web is a step backward for software development, and I think it conditions people to a different sense of what “fast” and “slow” mean. Text editors were pretty well sorted out by the 1990s, and fast, but now we’ve decided to make them slow, because…the web or something.
The Sublime Beta someone mentioned is just their version 3 “beta” which is more the new sense of beta as “something very stable that we just haven’t gotten around to stamping as 1.0 yet”
Brackets is also very nice, and has plenty of markdown support from its extensions. However, it will be more on the live preview, more of a visually oriented Adobe tool that is super pretty and focused on web dev almost exclusively.
All that said, I don’t think there’s anything better than StackEdit right now. I think the best markdown editors are online at this point. They have diagrams and other rich features. You might not need all that for your workflow, but I’m just impressed with them.
multimarkdown composer here. split screen realtime preview.
with footnote too.