This is a community wiki answer. You can edit me with your improvements. Alphabetically sorted.
Inline
Inline editors differ from normal editors as they can edit the content directly, i.e. not placing it inside another element, or inside an iframe.
Aloha Editorinactive since May 2016- CKEditor – starting from CKEditor 4 Beta
- Etch
FresherEditorinactive since November 2012- Hallo
HTML5 Editinactive since July 2011Mercuryinactive since December 2013- NicEdit
- Quill – starting from v0.19
- RedactorJS
- TinyMCE when used with Inline mode
- wysiwyg.js
- medium.js (library independent)
- ContentTools (Library independent)
- Froala WYSIWYG (jQuery)
- Trix
- Trumbowyg (jQuery)
- editable.js
- wysihtml
Iframes
Iframe editors often load the editor or content to edit into an iframe, to avoid styling conflicts.
- bootstrap-wysihtml5
- CKEditor
Mercuryinactive since December 2013- TinyMCE
WYSIHTML5inactive since December 2014