Exemplary PHP web applications with open source tools for learning?

I really liked the yii-framework. He's not as monstrous as Zend, but it is written very well.

I will add symfony2 and Doctrine 2.

CodeIgniter documentation competent

Definitely worth the download most famous framwork and see they are open and usually written very well =) I think this is the best option

> web application source code which will help in self-learning.
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\rpear.php.net — I at the time was very helpful, including training

A very interesting dev.lithify.me/lithium. Opportunities php5.3 (including namespaces, interesting implementation of classes). In General, much more interesting reading. By the way, this product is one of the creators of MongoDB

Learn frameworks and may the force be with You!
PS: I recommend to pay attention to Kohana 3.0 and 3.1