Update:

We have a winner! Alissa McGee suggested Joplin, which:

• is 100% completely free (but feel free to donate)
• works on all platforms: Windows, Linux, macOS, iOS, Android
• synchronises notes across your devices*
• has a split markdown preview / editing layout
• provides standard notebooks and tags features
• has language-specific syntax highlighting in code blocks
• supports mass-exporting of notes to multiple formats (markdown, JSON, etc.)

* by connecting to Dropbox, OneDrive, Nextcloud, WebDAV, or others

I guess I have a new markdown editor! Thanks, Alissa!

I've started to grow a bit weary of my current markdown editor, Simplenote. While it's fully cross-platform (Windows, Linux, macOS, Android, iOS) and auto-syncs your notes, it's markdown rendering can be a bit ugly and finnicky. So I decided to look for a new markdown editor.

Requirements:

• must be cross platform (at minimum: Windows, macOS, Android)
• ideally free
• ideally has a preview pane which updates instantly

I've looked through lots of pages of recommended markdown editors and here are most available markdown editors as of March 2019:

Cost and Cross-Platform Availability

Standalone (App) Editors:

* macOS version is free during beta testing
** 10.7 through 10.11
^† free during beta, will be $30 with v1.0
^†† free on Android, $8.99 on iOS, $19.99 on Windows, $28.99 on macOS
^‡ experimental / beta

Note that lots of IDEs / code editors have support for markdown, as well, including Atom, VS Code, Brackets, and more.

In-Browser Editors:

In-browser editors, by default, work on all platforms because they run in a web browser. Here are some common browser-based markdown editors:

Which one is right for me?

When I say "me", I mean me personally. I need an editor that works on Android, macOS, and Windows, at minimum. That kills most of the options above. What I'm left with is:

I've removed most of the in-browser options, as well, because they don't offer some features I really need (saving and syncing notes automatically). This doesn't leave much to work with.

Inkdrop is almost $50 per year, though they offer a 60% discount to students and educators (which I would avail of). Still, this would cost over $50 by my third year of use and would only continue to rise in price after that.

iA Writer charges for each platform you want to install it on, so it could end up costing me almost $50, though that is for a lifetime installation. The markdown editing works pretty well in it, though I don't like that you have to put an empty line before the beginning of a list.

Simplenote is my current editor. The markdown formatting has a few ugly bugs which cause lists to be spaced weird or not detected. This was the reason I was looking for a new editor in the first place.

StackEdit seems fine but also a bit of work (I need to connect it to a Dropbox account or something similar to sync my notes). I can't be asked to do this on each machine I'm working on. I might as well just edit my notes directly from Dropbox.

Woe is me

So I'm right back to where I started. Recently, I began playing around with Boostnote, which is a beautiful editor that used to be available for Android, though they've recalled this support. It is still available for all desktop platforms.

I guess I'm stuck with either Simplenote or Boostnote if I don't want to shell out $50 for a markdown editor. There may be hope for Boostnote, though, as it's currently under very active development. Maybe they'll re-open the Android version soon...