In Joomla! 1.5, you'll notice:

• Substantially improved usability, manageability, and scalability far beyond the original Mambo foundations

• Expanded accessibility to support internationalisation, double-byte characters and right-to-left support for Arabic, Farsi, and Hebrew languages among others

• Extended integration of external applications through Web services and remote authentication such as the Lightweight Directory Access Protocol (LDAP)

• Enhanced content delivery, template and presentation capabilities to support accessibility standards and content delivery to any destination

• A more sustainable and flexible framework for Component and Extension developers

• Backward compatibility with previous releases of Components, Templates, Modules, and other Extensions