Hello Joomla!

As of November 2011, there are over 8,600 free and commercial extensions available from the official Joomla! Extension Directory and more available from other sources.
Joomla History

• Joomla was the result of a fork of Mambo on August 17, 2005. 
• Joomla 1.0 was released on September 16, 2005. 
• Joomla version 1.5 was released on January 22, 2008. 
• Joomla 1.6.0 was released on January 10, 2011. 
• Joomla 1.7.0 was released on July 19, 2011, six months after 1.6.0. 
• Joomla 2.5.0 released on January 24, 2012 (six months after 1.7.0). This version is a long term support (LTS) release.

Core Features

• User Management : support multiple protocols, including LDAP, OpenID, and even Gmail. 
• Media Manager 
• Language Manager 
• Banner Management 
• Contact Management 
• Polls 
• Search 
• Web Link Management 
• Content Management 
• Syndication and Newsfeed Management 
• Menu Manager 
• Template Management 
• Integrated Help System 
• System Features 
• Web Services 
• Powerful Extensibility

NEW FEATURES IN JOOMLA! 2.5

http://www.joomla.org/25

• Smart Search Function : Based on Finder, which was developed by jXtended, Joomla 2.5 has added an exciting new natural language search function. This feature incorporated auto-completion and stemming. 
• Support Other DBs 
• Update Notification 
• Database Version Fix Button 
• CAPTCHA in Core 
• Linking New Menus with a Module : In Joomla 2.5, if there is no module associated with the menu, there is a link showing in the Menu Manager that you can click that will take you directly into a new module that you can create. 
• Use the Images and URL Fields to Create Simple Standardized Layouts 
• Choose whether Administrator to Get Email When New Users Register 
• Menu Item Note 
• Custom Text Filters 
• Manager for Language Overrides 
• User Note 
• Flexible Newsfeed Order 
• Image Option for the Offline Page 
• Improving SEO 
• ...

Joomla MVC Model

References:

1. http://en.wikipedia.org/wiki/Joomla
2. http://www.joomla.org/