CKEditor 5 is also worth a look. They just released their first alpha version. The editor now uses a model separate from the DOM which can be used to implement support for collaborative editing. In addition to providing an extensive API, there are ready-made builds which can serve the same purpose as TinyMCE and CKEditor 4. This being CKEditor, we can probably expect support for pasting content from Word and Excel in the future. GPL/LGPL/MPL. We've just started using it in our SaaS product and have been impressed so far. https://github.com/ckeditor/ckeditor5-design/issues/181