CKEditor (formerly FCKeditor) is an open source WYSIWYG text editor from CKSource that can be used in web pages. It aims to be lightweight
Using this facility Admin(end user) of site can modify contain of webpage
Because CKEditor is licensed under flexible Open Source and commercial licenses, you'll be able to integrate and use it inside any kind of application. This is the ideal editor for developers, created to provide easy and powerful solutions to their users.
To see the demo: http://ckeditor.com/demo
To download editor: http://ckeditor.com/download
For more information and documentation : http://ckeditor.com/