SimpGB
A guestboook script written in PHP. Features: Data stored in MySQL, admin interface, support for multiple languages, support for multiple instances in one database, multiple layouts, own header can be defined, support of BBCode and smilies, flood protection, IP banlist, bad word list, admins can write comments on posts and decide which input fields to display and which of them are required, support for avatars, email notification upon new posts, optionally validate new posts before they get visible by public, option to mark posts as private, search entries, admin can attach file to post and option to let users send emails directly in guestbook.