CCK is a module originally developed for Drupal that lets you easily create custom content types (for example, an article that also has additional fields for collecting location info about where the article took place, or a video, and displaying it as part of the article).
K2 is JoomlaWorks’ (http://www.joomlaworks.gr) version of CCK for Joomla and is completely open source.
Some additional details:
http://extensions.joomla.org/extensions/core-enhancements/content-management/8061/details
My thought was that if Joomlart helps this project out with perhaps a few bug fixes/feature additions AND they start integrating some K2-specific work into their new designs (or even backporting some functionality into older ones) that it would be really great for us current template club members, but it would also help grow the Joomlart community I think.