b2evolution is among the more popular open source blog program similar to others like Wordpress, e107, Joomla etc.. It is easy to setup and maintain and it only requires a web server with PHP and MySQL , b2evolution has gone through many years of development and it is still actively supported by the core team, it is a matured open source program and has gathered a large group of users over the years.
b2evolution blog tool is a powerful yet simple to use program, it can support single blog site or multiblog site setup with flexible user access control built in.
b2evolution is design to be modular which allows third party code contribution, and there is already a library of modules and plugins available to extend the features of b2evolution. The program has separated the content layer and presentation layer, and that has brought in lots of contributed free themes and templates to enhance the look and feel of your blog.