Node.js is a modern web development platform since it is new it is constantly getting mature day by day. Today not much open source apps are available which are built on Node.js but I found a promising CMS PencilBlue based on Node.js looks good.
PencilBlue is completely modern web CMS it has built-in support for MongoDB, AngularJS, Bootstrap, jQuery and completely responsive means ready for every screen sizes i.e. Mobile, Laptop, Desktop.
The best thing about this CMS is that it is lightweight, fast, scalable and extendable so you can use it not just for blogging but for complex website as well, however since it is new and open source as it’s uses increase with help of developer community definitely it will also become robust over the period of time like WordPress.
You can download it and try it by yourself.