phpblaster

phpblaster is a small, modular PHP-based portal system.

From the website:

phpblaster is a small but powerful and completely module based, portal system with focus on both, newbies and advanced users. The project started in June 2003 and is under ongoing development. After leaving the beta phase behind, it now runs on many professional pages and people are going to love it more and more.

You can easily add your themes into the themes folder and spot the places in your html code where you want to have the portal's functionality. With some basic PHP skills you can do a lot of cool things with it because it is really open! phpblaster's structure is similiar to portal systems like phpNUKE. This means that you could also easily port your phpNUKE modules to phpblaster and offer them to a wider audience.

Ew. I'd give it a wide berth.

UPDATE

Website is no longer online. As a matter of fact, the old site is now being remade using Joomla!...hehe