Free PHP Guestbooks

Chipmunk Guestbook
Chipmunk Guestbook is an easy to use yet powerful guestbook with a customizable layout, ability to delete entries by browse and search. MySQL required.

Ardguest - Free PHP Guestbook Script
Ardguest is a simple guestbook script that uses a flatfile to store messages, so you don't need any database like MySQL or PostgreSQL.

BIG SAM - PHP Guestbook
Built-In Guestbook and Stand-Along Module that requires php but does not need a database, allows visitors to leave their name, e-mail and comments on your web site. Features web-based administration of the guestbook.

Simple PHP Guestbook
This is a very simple guestbook done in PHP, named as Simple PHP Guestbook. It does not use SQL database but a text file to store entries and is distributed under GPL license

NBook - A guestbook script
NBook is a simple to use, simple to install guestbook script with web-based configuration. Fields are Name, Email, Homepage, Location, and Comment. Date and Time are added after posting and the users IP is hidden in a comment.