Notepad++ - A free source code editor which supports several programming languages running under the MS Windows environment.
Typora - A minimal Markdown reading & writing app.
Smultron - Smultron is an elegant and powerful text editor for macOS that is easy to use.
Dillinger - joemccann has 95 repositories available. Follow their code on GitHub.
Sublime Text - Sublime Text is a sophisticated text editor for code, html and prose - any kind of text file. You'll love the slick user interface and extraordinary features. Fully customizable with macros, and syntax highlighting for most major languages.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.