Lars Ellingsen's Guestserver - Supports several languages & multiple users. - http://folk.ntnu.no/larsell/guestbook/
Free Perl Guestbook (FPG) - A one-file-program guestbook written in Perl. It is multilingual and easy style editing, with built-in Banner Killer for using on Free Space Providers. [Freeware] - http://www.vitinh.de/cgi-bin/download_guestbook.cgi
Active Guestbook - A free guestbook. - http://www.active-scripts.net/
Rock13.com Webhelp - gb.cgi - Distribution site for gb, a simple Perl CGI guestbook. - http://rock13.com/webhelp/perl/gb/
VizBook - A guestbook list style Unix cgi script written for Perl 5 requiring Sendmail. [Freeware, if use the script as is without changes] - http://www.dtp-aus.com/cgiscript/vizbook.shtml
Jason's Guestbook - Includes automatic e-mail features. - http://www.aestheticsurgerycenter.com/scripts/guestbook/
DoubleMessageBoard - message board cgi. it is more than a guestbook and less than a full fledged bbs. - http://visitware.com/sobaya/dmb0.html
Gbook.cgi - Perl Guestbook CGI Script for use on Unix (Linux) web servers. Highly configurable look. Allow or deny HTML tags. - http://www.patrick-bernau.de/gbook/
BigNoseBird's Guest Book - fairly easy and versatile, with many useful features. - http://bignosebird.com/carchive/bnbbook.shtml
Guestbook*Star - Lets create a Guest-book and its CGI with no programming experience. - http://www.webgenie.com/Software/Guestar/