The Yii project was an attempt to fix some drawbacks of the PRADO framework. For example, in its early versions PRADO was slow when handling complex pages, had a steep learning curve and many controls were difficult to customize, while Yii was much more efficient at that time. In October 2006, after ten months of private development, the first alpha version of Yii was released. On December 3, 2008, Yii 1.0 was formally released.
January 2010 Yii 1.1 was released featuring form builder, relational ActiveRecord queries, unit testing framework and more. At the end of 2010 feature list for Yii 1.2 was on internal discussion. In May 2011 team decided to use new PHP versions and fix architectural mistakes. That basically meant 2.0. Same month the first commit was made. In May 2013 Yii 2.0 code went public. In October 2014 the first stable release of Yii 2.0 happened.
The Yii project has an extension repository consisting of user-contributed components.
There was also an official extension library, zii, which was then merged with the core framework. It is bundled in every release since Yii version 1.1.0, and it includes additional behaviors and widgets, such as grids and jQuery UI.
Yii comes with a collection of official documentation, such as a tutorial to develop a simple blog application, a guide that gives the description of every feature and a class reference which gives every detail about properties, methods and events.
There's also a user-contributed documentation, most of which is available within the wiki on the official website.
The text contained in the Official Yii Documentation is licensed to the public under the GNU Free Documentation License (GFDL). In general, the Yii documentation content can be copied, modified, and redistributed so long as the new version grants the same freedoms to others and acknowledges the authors of the Yii documentation article used.
The logo is licensed under a Creative Commons Attribution-No Derivative Works 3.0 Unported License.