Ghost started out as a Kickstarter project, with the aim of bettering WordPress. Ghost is run by a non-profit organisation, and released the source code today under the MIT license. Ghost is also run as a service, so you can create an account at ghost.org and try it out without having to install it.
However, fortunately it is pretty easy to install:
npm install --production and
npm start should get it running. It's easy because Bookshelf.js is database agnostic, so if your system has SQLite then it should be able to use it to store posts and users.
Event better, the fact Bookshelf.js is based around Backbone.js means you should be able to start hacking Ghost without much trouble. If you've done any work with Express and Backbone.js then Ghost's source will be eminently hackable.
The project is split into client and server code, and it uses popular patterns like promises, Express route separation, and Express middleware.
The architecture of the project has been shaped by the need to allow people to easily install and theme Ghost blogs, which means it deviates from the typical Express applications I write which are bespoke services. The focus on theming came from the need to create a similar designer-friendly ecosystem that WordPress has, and already on launch themes and services that sell themes are available. You can read more about this in Ghost Launches to The Public.
The fact the project started off as a Kickstarter project with hundreds of eager alpha testers means it already feels mature. And unlike many open source projects it has a dedicated team and a business model behind it, so it's definitely off to a promising start. I recommend giving it a look over if you're an Express developer or just tired of your own blogging platform.