Weblog software (also called blog software or blogware) is a category of software which consists of a specialized form of Content Management Systems specifically designed for creating and maintaining weblogs.
Free/Libre/Open-Source software
These software packages are offered under a Free/Libre/Open-Source Software license. Therefore they are free for everyone to use. Also, commercial support contracts are often available.
Apache Roller (Java-based)
b2evolution (PHP/MySQL)
bBlog (PHP/MySQL)
Beta-Blogger (PHP/MySQL or text files)
blojsom (Java-based)
blosxom (Perl)
PyBlosxom (Python)
Dotclear (PHP/MySQL)
Drupal (PHP/MySQL)
Elgg (Linux, Apache, MySQL, and PHP)
FlatPress (PHP/Flat Files)
Geeklog (PHP/MySQL)
Horizon Blogging Software (PHP/MySQL)
Livejournal (Perl) (Also available, developer hosted)
LifeType (PHP/MySQL)
Mephisto (Ruby on Rails)
Nucleus CMS (PHP)
Pivotlog (PHP)
Serendipity (PHP/MySQL,PostgreSQL,SQLlite)
SimplePHPBlog (PHP/Flat Files)
Slash (Perl)
Subtext (C#/ASP.NET)
Textpattern (PHP/MySQL)
WordPress (PHP/MySQL) - also offered in developer-hosted form as Wordpress.com
Proprietary software
These packages are under a proprietary license. They may require the purchase of a license key to use them. The specific licensing terms vary but some are free for personal or non-commercial use.
Community Server (also offered in developer-hosted form as CommunityServer.com)
ExpressionEngine (formerly pMachine)
Movable Type (also offered in developer-hosted form as TypePad)
Radio UserLand
Traction TeamPage
Unknown license
Battle Blog
Blogsphere