Big Sam is a built-In Guestbook Stand-Alone Module. It is a Guestbook that you just have to place on your public html files directory.
ffGuestBook is a PHP program which provides you a guestbook for your website. Everything it needs is a PHP capable webserver (nowadays almost all are) and some file storage on it. ffGuestBook has also an administation interface where the webmaster can edit (moderate) and delete entries.
Keep It Simple Guest Book
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.
The Sethi Family Guestbook is a multi-format guestbook script written in PHP. It features page spanning, (optional) private comments, user-selection of number of entries per page to display, multiple guestbook formats (elegant, simple, or standard), and background color. No database is required.
Simple Best Practices Guestbook
Simple Best Practices Guestbook (SBPG) is a project to show some of the best practices and technologies used in a simple guestbook written in PHP.
The SPPGuestbook is a very plain guestbook script. It uses a single flat file for saving the guestbook entries. It is easy to install and highly adjustable to any Web page layout.
YaBook is a powerful PHP 5 guestbook that features easy installation and customization, multi-language support, an administration interface, moderation of new submissions, and URL obfuscation. Various database systems are supported. The script auto-detects a new installation and performs incremental upgrades if required.