Quill was built to address the problem that existing WYSIWYG editors are themselves WYSIWYG. If the editor was not exactly the way you want it, it was difficult or impossible to customize it to fit your needs.
Quill aims to solve this by organizing itself into modules and offering a powerful API to build additional modules. It also imposes no styles (though reasonable defaults are available) to allow you to skin the editor however you wish.
Quill also provides all of what you’ve come to expect from a rich text editor, including a lightweight package, numerous formattingoptions, and wide cross platform support.