TotalFinder - TotalFinder is a plugin for Finder.app which adds tabs like in Chrome browser, dual panels similar to TotalCommander and more tweaks.
Typora - A minimal Markdown reading & writing app.
Path Finder - The Finder, reinvented. Path Finder is an award-winning file browser and management application for Mac OS X.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
Forklift - The most advanced dual pane file manager and file transfer client for macOS.
MarkText.app - Mark Text is a Markdown editor for Mac, Windows and Linux.