Fred Wu has put together a comparison of three of the more well-known PHP frameworks out there - CodeIgniter, Kohana and the relative newcomer Yii.

It was over a year ago that I wrote the article that compares CodeIgniter and Kohana. Since then both CodeIgniter and Kohana have seen major progress with the release of CodeIgniter 1.7.0 and Kohana 2.3. [...] Let's see how they compare with each other.

He judges on a list of criteria including licensing, supported databases, community, documentation and modularity. Ratings are gives for each framework (like "Excellent" or "Good") on each item with over twenty aspects considered.