PHP

esoTalk – Modern Forum Software Based on PHP & MySQL
esoTalk is free, open-source Internet forum software which focuses on removing the complexity of forum apps with a simple, modern interface and functionality. it is built based on PHP and MySQL.

Open Source Social Services Authentication Library : HybridAuth
HybridAuth is an open source authentication and authorisation solution that combines the strengths of several major social networks and ID (Identity Providers) services into one simple PHP Library.

Open Source File Manager Built with jQuery and PHP : SFBrowser
SFBrowser is an open source file manager (browser and uploader) built with jQuery and PHP for managaing files with an Ajaxed interface. It returns a list of objects with containing the names and additional information of the selected files. You can use it, like any open-file-dialog, to select one or more files.

A Clean and Classy PHP Framework : Laravel
Laravel is a clean and classy framework for PHP web development. Freeing you from spaghetti code, Laravel helps you create wonderful applications using simple, expressive syntax.

TCPDF – A Complete Features PHP Libs for Generating PDF Documents
TCPDF is a FLOSS PHP class for generating PDF documents. It’s free, open Source and now one of the world’s most active Open Source projects

Fuel – Simple, Flexible, Community Driven PHP 5.3 Web Framework
Fuel is a simple, flexible, community driven PHP 5.3 web framework based on the best ideas of other frameworks with a fresh start. It was born out of the frustrations people have with the current available frameworks and developed with support from a community of developers.

Zebra Form – A PHP Class for Creating & Validating HTML Forms
Zebra_Form is a PHP class that simplifies the process of creating and validating HTML forms. Its object-oriented structure promotes rapid HTML forms development and encourages developers

Use PHP Functions in JavaScript with php.js
php.js is an open source project that brings high-level PHP functions to low-level JavaScript platforms such as web browsers

xmoovStream – Open Source HTTP Streaming Server Based on PHP
The xmoovStream Server (formerly known as xmoov-php) is a centralized http streaming server written in PHP.

osTicket – Open Source Customer Support Ticket System based on PHP & MySQL
osTicket is an open source support ticket system that is used widely based on PHP and MySQL.