A blog (a contraction of the term "Web log") is a Web site, usually maintained by an individual with regular entries of commentary, descriptions of events, or other material such as graphics or video. Entries are commonly displayed in reverse-chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
Many blogs provide commentary or news on a particular subject; others function as more personal online diaries. A typical blog combines text, images, and links to other blogs, Web pages, and other media related to its topic. The ability for readers to leave comments in an interactive format is an important part of many blogs.
http://en.wikipedia.org/wiki/Blog

Anchor is a content management system, built especially for art-directed blogs.

Chyrp is a blogging engine designed to be very lightweight while retaining functionality. It is powered by PHP and has very powerful theme and extension engines, so you can personalize it however you want.

A CakePHP powered CMS

DotClear was design only for weblogs management, and do it well. It is completely free! DotClear is a free software distributed under the GNU General Public License.

FlatPress is an open-source standard-compliant multi-lingual extensible blogging engine which does not require a database to work. You don’t need MySQL because FlatPress stores all of its content on text files. All you need is a PHP-enabled web space.

While there are a number of technical reasons that highlight the differences and advantages Habari has over other blogging packages, a major component of what makes Habari different is its community participation model.

The goal of the LifeType project is to create a stable multi-user and multi-blogging platform, to strengthen the concept of communities around blogs.

LiveStreet is a free engine for blog and social networks.
The project has been implemented with the object oriented programming on PHP5 + MySQL5 and is built on the principle of the MVC model.

Nibbleblog it's a powerful engine for creating blogs, all you need is PHP to work. Very simple to install and configure (only 1 step).

With Nucleus, you can set up one or more weblogs. If you want to, you can even show the contents of multiple weblogs on the same page. Each blog has its own team of authors.