I use Joplin. It can sync across Windows, OS X and iOS (didn't try it on Android), notes are in Markdown. The note editor is not awesome, compared to smth like

I use Joplin. It can sync across Windows, OS X and iOS (didn't try it on Android), notes are in Markdown. The note editor is not awesome, compared to smth like Typora, but it's ok if you just want to type in Markdown.