Zettlr - Write Markdown documents with a comprehensive GUI and many workflow/time management tools.
MacDown - MacDown is an open source Markdown editor for OS X, released under the MIT License.
Typora - A minimal Markdown reading & writing app.
MarkNote - A simple markdown note management app.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
MarkText.app - Mark Text is a Markdown editor for Mac, Windows and Linux.