Free FAQ / Knowledge Base PHP Scripts

FaqForge

FaqForge allows you to create and manage online FAQs, manuals, HOWTO documents and the like. It is released under the GNU General Public License. There is no mention of whether it requires SQL support (whether MySQL or otherwise) or not.
phpFAQTory

This PHP FAQ or knowledge base manager requires you to have MySQL. You can apparently create users who have different access rights (eg, those who can only ask questions and read the answers, others who can post answers). It is released under the GNU GPL. The site is in French.
my Knowledge Base

Create a knowledge base for your site with this PHP 4 script. You need a MySQL database. The knowledge base script comes with an installation script that apparently allows you to install the script without mucking around with the script itself.
FAQ-U

This FAQ script allows you to maintain your FAQs dynamically. It comes with an installation script to simplify your installations. It requires PHP. The site does not have much information about the script, so I do not know about the database requirements. It is no longer under development.
The Knowledgebase

You can organise your knowledgebase by topics with this PHP script. Visitors can also browse through the knowledgebase using keywords. This script requires PHP, MySQL and an Apache web server. It is distributed under the GNU General Public License.