Habari
I first heard about this project in episode 18 of the WordPress Podcast. It is called Habari, which means ‘news’ in Swahili (I guess using african words for names is part of the the new web 2.1 
).
Here’s what they have to say for themselves:
Habari represents a fresh start to the idea of blogging. The system is fast, easy to use, and easy to modify. New users should have no problem using and enjoying Habari. Advanced users should have no problem tweaking Habari to do exactly what they need it to do. Habari relies on PHP5 with PHP Data Objects (PDO), and your choice of SQL database (MySQL, PostgreSQL, SQLite).
Habari is strongly object oriented, and implements the full suite of the Atom Publishing Protocol. User-created plugins make Habari do nearly anything imaginable, and a robust theme system permits the use of several popular templating solutions.
While I’m one of the biggest fans of WordPress, I must say that this sounds really interesting, and starting fresh using the latest cutting edge technologies is a great idea, and the result will probably be super-cool.