CKEditor - Real-time collaborative future-ready rich text editor
TinyMCE - TinyMCE is a content editor that functions as a plug-in for Wordpress websites.
WYMeditor - WYMeditor is a web-based WYSIWYM (What You See Is What You Mean) XHTML editor (not WYSIWYG).
Trumbowyg - Feature-packed WYSIWYG editor in only 15kB of JavaScript
Editor.js - A block-styled editor with clean JSON output
Quill - Powerful, API-driven rich text editor