Ghost is an open-source blogging platform, developed with NodeJS and Express, that has an emphasis on easy installation and theme development.
Ghost acquired funding through Kickstarter; many beta testers have ensured that Ghost already feels quite fine around the edges. Its source code was released yesterday.
Ghost is very easy to install, and experienced Express developers will find that they can read the code quite fluently.
P.S. You can also give Ghost a spin at the homepage.