FreeTextBox - FreeTextBox is the most-used free ASP.NET WYSIWYG HTML editor featured in open source and commercial projects.
CKEditor - Real-time collaborative future-ready rich text editor
Froala Editor V2 - A beautiful modern WYSIWYG HTML text editor
Trumbowyg - Feature-packed WYSIWYG editor in only 15kB of JavaScript
Edtr.io - Intuitive WYSIWYG web editor, open source & fully adaptable.
TinyMCE - TinyMCE is a content editor that functions as a plug-in for Wordpress websites.