It 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... Not to mention third party plug-ins!
Plus, it's free, open-source (GPL), it runs on virtually any webserver featuring PHP+MySQL and it's available in many languages!

You can test the latest version on http://test.b2evolution.net/ - this is especially useful for reproducing bugs etc.