Framework written in PHP

http://zeronotice.org/

http://wildweb.sourceforge.net/

WildWEB is an open source framework for web application development.

http://wtfw.sourceforge.net/

https://symfony.com/

Symfony is a set of reusable PHP components... The standard foundation on which the best PHP applications are built. Choose any of the 30 stand-alone components available for your own applications.

http://mojavelinux.com/projects/studs/

http://www.seagullproject.org/

http://phphtmllib.newsblob.com/

http://nutexframework.sourceforge.net/

http://midgard-project.org/

http://ismo.sourceforge.net/

Ismo is an application framework written in PHP for PHP. It features industry accepted design solutions such as MVC (model-view-controller separation) yet remains easy and straightforward to use.