Joomla 3.x is a mature release of the Joomla platform that has been completely redesigned from the ground up. Major new features include unlimited nested content categories, and access control to site content and functionality through custom user groups. The admin interface has been compleely revamped, an under the bonnet everything is shiny and new, and built with the developer in mind. For custom built web application development, Joomla 3.x is simply unsurpassed by any other open source platform, and rivals most proprietary solutions as well. The price of this leap forward is backward compatibility. Moving from Joomla 1/2 to Joomla 3.x is a big migration, and will involve conversion of templates, components and plugins as well as all content. Depending on the complexity of your website, this could be a very involved process.
