CodeIgniter

Here are the slides to an interesting talk about PHP frameworks, given by the "first" creator of PHP, Rasmus Lerdorf, who now works for Yahoo.

In PHP 3.0+, Rasmus kind of gave up control of PHP to a couple other guys who took it in much more of a Object-oriented way. I like the following slides where Rasmus questions how 10 years of OO haven't added much (except confusion) to the language :

http://talks.php.net/show/drupal08/4 PHP 1995 - short and simple
http://talks.php.net/show/drupal08/5 PHP 2005 - after 10 years of OO cruft added