What are some alternatives?
When comparing Atom and StackEdit, you can also consider the following products
Visual Studio Code - Build and debug modern web and cloud applications, by Microsoft
Typora - A minimal Markdown reading & writing app.
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.
iA Writer - Minimal Design, Maximum Focus
Vim - Highly configurable text editor built to enable efficient text editing
Haroopad - Haroopad is a markdown enabled document processor for creating web-friendly documents.