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P4A (PHP For Applications) is a PHP5 RAD and object oriented PHP framework for building event-driven stateful web applications. It is based on Zend Framework and features tableless HTML, multiple databases, accesskey support, auto data type recognition, transparent AJAX, UTF-8, i18n/l10n.
P4A is empowered by Zend Framework, jQuery, jQuery UI and FCKEditor and is:

100% PHP5 […]

Kohana is a PHP 5 framework that uses the Model View Controller architectural pattern. It aims to be secure, lightweight, and easy to use.

Features

Highly secure
Extremely lightweight
Short learning curve
Uses the MVC pattern
100% UTF-8 compatible
Loosely coupled architecture
Extremely easy to extend

Technology

Strict PHP 5 OOP
Simple database abstraction using SQL helpers
Multiple […]

Mmslib is a PHP library for encoding and decoding MMS:es. MMS is short for Multimedia Messaging Service. In short it is the successor of SMS (Short Message Service) with the enhancements that you can not only send text but basically any content type your phone can handle such as images, text, videos, ring signals and […]

Previously I have written on Volantis and MyMobileWeb as a mobile content delivery platform.
If you are looking a PHP based CMS for mobile, then you can plug-ins then you can add to the existing CMS to make the content mobile compatible.
Wap-2-Go is a add-on module to PHPNuke.  It is a Mobile Content Management System (CMS) […]

Adhere Mobile Advertising Platform is a suite of software products that serve the needs of the mobile advertising community. At the core of the platform is the free open-source Adhere Ad Server. The platform also includes the Adhere User Profiles Server which is key to Adhere’s ad targeting capabilities. Finally, the platform includes sample applications […]

OASIS is a high-performance ad server built using Linux (RHEL4), Apache, PHP, and MySQL. It is designed to handle many hundreds of thousands of ad impressions per hour. On moderately capable dual processor hardware, it is capable of serving approximately 500,000 impressions per hour.
With OASIS, a publisher, network or marketer can manage all of […]

Recently I have a try on WordPress MU and I was impressed.
With WordPress MU, you can run hundreds of thousands of blogs with a single install of WordPress.
Features

Everything WordPress does.
Scaling to tens of millions of pageviews per day.
Unlimited users and blogs.
Different permissions on different blogs.
Ambiguity about how to pronounce its name

It is suitable for

Newspapers […]

Beehive is an open-source project for creating a high-configurable frame-based discussion forum.
Beehive Forum has a lot of features. The main ones are listed below:

Frame-based layout, for easy navigation.
Reply-to-user posting and e-mail notification.
Powerful HTML posting, without security risks.
Extendable user profiles.
Flexible relationships system.
Private Messaging system.
Multiple style options, including dyslexia support.
Advanced word-filtering facility.
Comprehensive user permissions.
Full, easy to use […]

TestLink enables easily to create and manage Test cases as well as organize them into Test plans. These Test plans allow team members to execute Test cases and track test results dynamically, generate reports, trace software requirements, prioritize and assign tasks.
The tool has web based interface with PHP and background database MySQL, Postgres or […]

eAccelerator is a free open-source PHP accelerator, optimizer, and dynamic content cache. It increases the performance of PHP scripts by caching them in their compiled state, so that the overhead of compiling is almost completely eliminated. It also optimizes scripts to speed up their execution. eAccelerator typically reduces server load and increases the speed of […]

phpQuery is a server-side, chainable, CSS3 selector driven Document Object Model (DOM) API based on jQuery JavaScript Library.
E.g.

// pq(); is using selected document as default
phpQuery::selectDocument($doc);
// documents are selected when created or by above method
// query all unordered lists in last selected document
pq(‘ul’)->insertAfter(‘div’);

/ 1st way
print phpQuery::getDocument($doc->getDocumentID());
// 2nd way
print phpQuery::getDocument(pq(‘div’)->getDocumentID());
// 3rd way
print pq(‘div’)->getDocument();
// 4th way
print $doc->htmlOuter();
// 5th […]

PhpGedView is a revolutionary genealogy program which allows you to view and edit your genealogy on your website. PhpGedView has full editing capabilities, full privacy functions, can import from GEDCOM files, and supports multimedia like photos and document images. PhpGedView also simplifies the process of collaborating with others working on your family tree. Your latest […]

PHP Simple DOM Parser

A HTML DOM parser written in PHP5+ let you manipulate HTML in a very easy way!
Require PHP 5+.
Supports invalid HTML.
Find tags on an HTML page with selectors just like jQuery.
Extract contents from HTML in a single line.

There is a gallery of best open source PHP projects at http://open.srcphp.com/

Open Source PHP is a community site dedicated to tracking the best open source PHP projects.
OpenSrcPHP.com features an easy to browse gallery of the best Open Source PHP projects.
Each project features screenshots plus community driven comments, ratings, and bookmarking.

TurboDbAdmin is a single-page solution for exploring and editing databases from a browser. Edit data just like you would in a desktop application, without submit buttons or page refreshes.

This is the free and open source ad server I am trying now.

As quoted, OpenX  is a hugely popular, free ad server designed by web publishers for web publishers. It provides everything you need to manage your online advertising.Make more money from online advertising today.
OpenX gives you:

Control  - Maximize your revenue by showing […]

This is the open source web analytics software in PHP that I recently tried. I am quite satisfied with the features it provided.
As quoted from the website, piwik is an open source (GPL license) web analytics software. It gives interesting reports on your website visitors, your popular pages, the search engines keywords they used, the […]

I have been using CakePHP 1.1 for few projects, and now I am so used to it and tend to use it for every PHP project that I am doing. CakePHP 1.2 is still in beta but more features are incorporated into the core. One of the features that I think should be part of […]

I have written my web application in PHP using CakePHP framework, and I need to reuse part of the code in a scheduled job for data extraction. To avoid coding in other language, I was trying to see if it is possible for me to use PHP and CakePHP to run a scheduled job.
To do […]

There are many open source PHP frameworks for rapid development. Each one has its own advocates and for beginner PHP developers it is really time consuming to learn and choose the frameworks that they are comfortable with.
IMHO, they are really no best frameworks. Every developer has his/her own preferences. Many may favor over one […]