PHP-Link Trader allows you to easily trade links with other sites. It keeps track of all incoming and outgoing hits and ranks the sites based on how many visitors they send to your site.
PHP-Ring is a web ring system that allows you to create and manage multiple rings about different topics. Hosting a webring on your site increases both traffic to your site and links to your site.
This php script allows you to add a completely customizable guestbook to your website. It uses templates and allows you to have mutliple guestbooks with just one installation.
I have released the code for the "latest encyclopedia entries" block for sites using php-nuke and the encyclopedia module. It can be downloaded from the here.
