xAMP

WordPress MU, or multi-user, is designed to do exactly that. It is most famously used for WordPress.com where it serves tens of millions of hits on hundreds of thousands of blogs each day.

Wheatblog is blogware: it's a web-based content management system for maintaining online blogs, journals, news pages, and about anything else you can think of writing down. It allows reader interaction with a comment system, and generates valid RSS 2.0 feeds. It is powered by PHP and is compatible with the MySQL and SQLite database systems.

Serendipity is a PHP-powered weblog application which gives the user an easy way to maintain an online diary, weblog or even a complete homepage. While the default package is designed for the casual blogger, Serendipity offers a flexible, expandable and easy-to-use framework with the power for professional applications.

Pivot is a web-based tool to help you maintain dynamic sites, like weblogs or online journals. Pivot is released under the GPL so it is completely free to use. It is written in PHP, and does not require additional libraries or databases to function.

LoudBlog is a sleek and easy-to-use Content Management System (CMS) for publishing media content on the web. It automatically generates a skinnable website and an RSS-Feed for Podcasting.

Geeklog is a PHP/MySQL based application for managing dynamic web content.

b2evolution includes all the features of traditional blog tools, and extends them with evolved features such as file & photo management, advanced skinning, multiple blogs support as well as detailed user permissions...