gelato cms is described as a tumblelog cms. It's based around the tumbr concept, you can easily post snippets. Various themes and plugins are available.
LifeType is a multi-user, multi-blog blogging platform. It started in 2003 and is up to date as at Mar 2008. Seems to support all the major features.
b2evolution is an open source PHP / MySQL blog platform. It seems to be more basic and less polished than the likes of WordPress, MovableType or Habari.
Serendipity is a PHP / MySQL blogging system. It uses the Smarty template engine.
Habari is an open source PHP / MySQL blogging platform (like WordPress).