TomatoCMS follow MVC architecture, object-oriented models (OOP) and design principles (Design Pattern). This Free CMS also held in the model of chemical module, and supports plugin/hook architecture. Programmers will be very easy to develop a module, plugin, hook or widget.

RubyFlow is a community site dedicated to sharing links related to a specific topic.

Storytlr is an open source lifestreaming and micro blogging platform. You can use it for a single user or it can act as a host for many people all from the same installation. Mashup your data from around the web into one place make it easy for others to follow your every social update.

TypePad Motion enables publishers and marketers to create vibrant, branded communities that deepen loyalty and increase page views while giving you total control of your brand. It is based on Pownce & MovableType Motion and built with Django.

PivotX is also a great open source tool to maintain more complex websites AND BLOGS. Its powerful core and flexible template system make it easy for developers to adjust and extend. No matter if you want an easy-to-use, robust blogging tool or are looking to push things to the max.

Plumi open source platform pulls together the following features on top of the out-of-the-box Plone functionality...

Automne is a free open-source Content Management System based on PHP and MySQL and available under licence GNU-GPL.
Automne manages content from entreprises, governement, educational institutions and non profit organizations on the web, intranet and extranet...

EZPX is a free lightweight photoblog engine having all the features you'd need and a user interface you'll love to use.

This PHP and MySQL script provides a simple and lightweight blogging/news system for your website. The script allows you to quickly post updates to your blog via an online control panel from which you can also manage your blog and prepare posts. This script is ideal to provide updates and information to your visitors about yourself, your website, company or product.