WSN Guest is a flexible PHP/MySQL guestbook script distributed under the free and permissive MIT license. Most of the development took place in 2003, but it continues to function well today. Take it and make commerical derivative works if you like. Make a post on the forum to share your improvements or sell your derivative product. Free web traffic is available to anyone who makes a derivative guestbook script -- this page can be redirected to yours.
Requirements: PHP 4.1.0+ (or PHP 5), MySQL 3+. A knowledge of HTML and CSS is very useful for taking full advantage of the template system.
Last version: 1.24
Documentation: See readme.txt.