CKEditor - Real-time collaborative future-ready rich text editor
Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
Redactor Text Editor - WYSIWYG html editor.
Typora - A minimal Markdown reading & writing app.
PHP Markdown - PHP port of the Markdown text-to-HTML conversion tool for web writers.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.