If you've worked with Yii in the past, be prepared. The new version of Yii 2 can be considered as a brand new framework, modern and robust.
Yii 2 takes a long-awaited step forward in the right direction. It is the result of several years of work, done collaboratively on the Internet, mostly on GitHub (https://github.com/yiisoft/yii2), by developers from different parts of the world.
As a user of Yii, you can collaborate too, by simply filing bug reports, feature requests at https://github.com/yiisoft/yii2/issues, polishing off the documentation and translations, and creating new extensions and features for review and inclusion on the project. There are also many other non-officially supported subprojects that can benefit from your support: some already there for you to use, and some that you may have written yourself.