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
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.
Edtr.io - Intuitive WYSIWYG web editor, open source & fully adaptable.
Froala Editor - Froala Editor is a WYSIWYG HTML editor that enables rich text editing capabilities for the applications.
Aloha Editor - Aloha Editor is an HTML5 WYSIWYG Editor that gives you a total new experience when editing.