Calipso is a simple NodeJS content management system, built along similar themes to Drupal and Wordpress, that is designed to be fast, flexible and simple.
For additional details, including installation instructions, please visit the home page: http://calip.so/
If you would like to contribute, please take a look at the issues list as this will have the most up to date view of work that needs to be done for the next minor release. Otherwise, please just pm myself (cliftonc) or dennis (dennishall) and we can suggest some places for you to start.