Our blog software is NOT OPEN SOURCE, but what it is is 100% CSS template, and 3 server side include lines, so you can customize it virtually any way you see fit.
Oh ... and you said easy?? You can be up and running in 3 minutes!
www.dblogger.com
(and did I mention that G and MSN love it ???? As we make most of our income from adsense/chitika and SEO, we wanted to build a simple yet effective blog software from the ground up!!)