ActiveKB
   A web based knowledge base application that allows users to manage their knowledge base or frequently asked questions. [Commercial]
   http://www.interspire.com/activekb/

Faq Manager Pro
   A FAQ and knowledgebase solution with easy installation. Full layout and design control. Multi-Language support. [Commercial]
   http://www.faq-manager-pro.com

Frequently Asked Questions Engine
   An open source PHP system which lets you make your FAQ dynamic in nature, easier to maintain, and searchable.
   http://www.codegrunt.com/

Idevspot iSupport
   A hybrid customer support script with a fully customizable template system, including support tickets, knowledge base, FAQ, customer testimonials.
   http://www.idevspot.com/index.php?page=p_detail~1

Knowledge Builder
   A knowledge base / FAQ solution for commercial and personal use.
   http://www.activecampaign.com/kb/

Lore
   An advanced knowledge base management system based on PHP, MySQL, and Smarty. [Commercial]
   http://www.pineappletechnologies.com/products/lore/

SocketKB
   A flexible knowledge base management system based on PHP and MySQL. [Commercial]
   http://www.socketkb.com

Softbiz FAQ Script
   Configurable, multidimentional FAQ script to run web sites FAQ Section. [Commercial]
   http://www.softbizscripts.com/FAQ-script-features.php

WSN Knowledge Base
   Customizable PHP/MySQL knowledge base script. [Commercial]
   http://scripts.webmastersite.net/wsnkb/

piFAQ
   A simple script that will help to create (and manage) FAQ page on site. It is based on PHP, MySQL and FastTemplate so it's fast and easy in configuration.
   http://pifaq.sourceforge.net/