K2 is a Content and CCK (content construction kit) Extension for Joomla! that provides more features than the standard content component.
K2 - Content and CCK
K2 is the popular and powerful content extension for Joomla with CCK-like features. It provides an out-of-the box integrated solution featuring rich content forms for items (think of Joomla articles with additional fields for article images, videos, image galleries and attachments), nested-level categories, tags, comments, a system to extend the item base form with additional fields, a powerful plugin API to extend item, category and user forms, ACL, frontend editing, sub-templates and a lot more!
K2 is available for free. There is a whole dedicated section of extensions (free and commercial) that are built specifically for K2 or with K2 support, that extends default K2 functionality or add integration with other Joomla extensions.
K2 is developed and maintained by JoomlaWorks