CKEditor

HTML

<script src="http://ckeditor.com/apps/ckeditor/4.0/ckeditor.js"></script>
<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/css/bootstrap-combined.min.css">
<script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/js/bootstrap.min.js"></script>
<div>
    If you press the indentation button repeated times, eventually the text 'Test' will leave the editor boundry instead of adding a horizontal scroll bar inside the editor. 
</div>
<br/>
<br/>

<div id="editor1" contenteditable="true">Test</div>

JavaScript

CKEDITOR.inline('editor1');