Jambook Joomla Guestbook
Jambook is a feature rich open source Joomla guestbook component with spam protection, email address cloaking, flood protection, double posting checks and the ability to use Joomla wysiwyg editor, even for guests!
Jambook uses AJAX in the backend to speed up some common administration tasks. As this is a component for the CMS Joomla you will obviously need Joomla to run this.
This component is released under the GNU General Public License, a copy of this license should be included in the zip file and available for reading from the administrator page once the component has been installed.
Just install the component as according to the Joomla documentation.