Yii framework

Not so long time ago I have learned php5 Yii framework
It is quite simple and well documented MVC  framework
I like it!

So why I think it will be popular?
because it is easy to use.. and it is free
Here is  few the most important features for me

Localization 
first of all I pay attention to frameworks localization
only one static function  

Yii::t("section", "string")

Security
It is very important to have only one entry point for all user requests
in this case you can wrap this entry with security patterns and framework itself already did it for you

All requests have the same entry for example


http://mysite.com/index.php?r=action&...

of cause you are able to create more attractive requests like


http://mysite.com/home/livingroom
http://mysite.com/2010/09/01/school

there is a trick.. all this urls redirect your request to one php file. remove php file entry name like "index.php" is done using .htaccess or if you are able to configure apache yourself it is could be done in *.conf file

Database
You are able to request data  from database even if you don't know sql and even if you are not sure what database is installed on you web server. I mean code that Yii framework produces is working with any sql database platform (MySQL, PostageSQL, SQLite or other PDO php extention. 
As results of the request it returns associative array and all other low-level stuff framework hides inside.

Widgets and Components
Widgets is a way to reuse you code - very powerful thing

I am not going to describe all Yii features, there is a manual for that