RadhikaGB is a guest book that is highly customizable and highly optimized. It features a powerful admin panel and spam protection. Users are able to update keywords, descriptions, per page posts, counter values, etc. RadhikaGB is highly secure, and it logs all login activity to the admin panel. It also has the builtin ability to back up its database.
GentleSource Guestbook allows you to put a guestbook on your Web site. Your visitors can sign it and leave a message. The entries can be edited and deleted in the admin area. In order to prevent the script from being abused by automatic spam bots, you can enable the CAPTCHA feature. Visitors have to ensure that their browser supports and accepts cookies, otherwise the comment cannot be verified.
DRBGuestbook is a simple PHP guestbook script that uses a flat file and does not require any additional database software. It supports an easy-to-use, Web-based administration interface. Features include flood protection, banning by IP address, a bad words list, email notifications, and multiple anti-spam features.