CKEditor - Real-time collaborative future-ready rich text editor
Edtr.io - Intuitive WYSIWYG web editor, open source & fully adaptable.
HTML Editor - Create HTML snippets with a simple WYSIWYG editor
TinyMCE - TinyMCE is a content editor that functions as a plug-in for Wordpress websites.
CoffeeCup HTML Editor - The CoffeeCup Free HTML Editor is a drag-and-drop HTML Editor with built-in FTP uploading.
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.