Blogs

b2evolution 1.9.2 A multilingual multiuser multi-blog engine.
Mephisto 0.7.3 Mephisto is a blog engine with some simple CMS-ish concepts (sections, pages) and a very flexible templating system.
Movable Type 4.1 The Movable Type platform makes it easy for you to both author content and interact with your community of readers.
Nucleus 3.32 Maintains multiple weblogs.
Textpattern 4.0.6 A free, flexible, elegant, easy-to-use content management system for all kinds of websites, even weblogs.
Typo 4.1.1 Typo is a lean engine that makes blogging easy.
WordPress 2.3.2 A semantic personal publishing platform with a focus on aesthetics, web standards, and usability.
WordPress MU 1.3.2 The multi-user version of the WordPress blog engine.

Calendars

PHP-Calendar 0.10.9 A web-based calendar and event scheduled written in PHP.
phpScheduleIt 1.2.8 A web-based resource scheduling system that allows administered management of reservations on any number of resources, such as conference rooms.
Plans 7.9.9 Plans lets you put calendars on the web.
WebCalendar 1.1.6 A PHP application used to maintain a calendar for one or more persons and for a variety of purposes.

E-commerce

Openads 2.4.3 Openads is an open-source ad server, with an integrated banner management interface and tracking system for gathering statistics.
osCommerce 2.2rc1 osCommerce is the leading Open Source online shop e-commerce solution.
PHPCoin v124 The phpCOIN (Clients, Order, Invoices, and Notes) package was designed for small to medium sized webhosting resellers.
SugarCRM 4.5.1h A powerful open-source package for managing customer relationships.
ZenCart 1.3.8 Zen Cart is a free, user-friendly, open source shopping cart system.

Community

AROUNDMe 0.6.9 AROUNDMe is the perfect solution for community builders wishing to bring together multiple mutual interest groups within a shared knowledge network.
bbPress 0.75 bbPress is forum software with a twist from the creators of WordPress.
CivicSpace 0.8.5 CivicSpace is a free open-source software platform for grassroots organizing and civic activity.
Drupal A full-featured content management/discussion engine suitable to setup a news-driven community or portal site.
IntegraMOD 1.4.1 IntegraMOD is a pre-modded version of phpBB with great modifications that are made compatible with each other.
phpBB A high powered, fully scalable, and highly customizable Open Source bulletin board package.
Simple Machines Forum 1.1.4 Simple Machines Forum (SMF) is a free, professional grade software package that allows you to set up your own online community within minutes.

Content Management System

Joomla ! Joomla! is a powerful Open Source Content Management System.
Mambo 4.6.2 Mambo is a powerful Open Source Content Management System.
Moodle 1.5.4 Moodle is a course management system (CMS) to help educators create effective online learning communities.
phpWebSite 0.10.2 phpWebSite provides a complete web site content management system.
PostNuke 0.764 A flexible Open Source content management system.
Radiant CMS 0.6.3 Radiant is a no-fluff, open source content management system designed for small teams.
Xoops 2.0.18 XOOPS is an extensible, OO, easy to use dynamic web content management system written in PHP.

Database Management

phpMyAdmin A browser-based MySQL database management interface.
phpPgAdmin 4.1.3 A browser-based PostgreSQL database management interface.

Email

cgiemail 1.6 The purpose of cgiemail is to take the input of WWW forms and convert it to an e-mail format defined by the author of the WWW form.
NMS::FormMail 3.14c1 NMS::FormMail is a generic HTML form to e-mail gateway that parses the results of any form and sends them to the specified users. It is a drop-in replacement for the older FormMail program.
PHPList PHPlist is a web application that implements a personalised mailing list manager or customer relationship management (CRM) system.
RoundCube 0.1-rc2 RoundCube Webmail is a browser-based multilingual IMAP client with an application-like user interface.

Guestbook

Advanced Guestbook 2.4.3 Advanced Guestbook is a PHP-based guestbook script.

Helpdesk

FAQMasterFlex 1.0 This is a database-driven application for creating and maintaining Frequently Asked Questions.

Horde

Horde 3.1.6 Horde is a framework for PHP applications. It is typically used in conjunction with other scripts such as IMP (for webmail) and Kronolith (for calendars).
Forwards h3 Forwards is a Horde module for setting user e-mail forwards with support for several popular mailers.
Kronolith h3 Kronolith is a PHP-based calendaring system, which is part of the Horde project.
MIMP h3 MIMP is a webmail client for mobile devices, which is part of the Horde project. Mnemo Mnemo is the Horde notes and memos application. It lets users keep free-text notes and other bits of information which doesn't fit as a contact, a todo item, an event, etc.
Nag Nag is the Horde task list application. It stores todo items, things due later this week, etc.
Passwd Passwd is the Horde password changing application.
Vacation Vacation is a Horde module for managing user e-mail vacation notices or auto-responders.

Photo's

Coppermine 1.4.16 Coppermine is a multi-purpose fully-featured and integrated web picture gallery script written in PHP.
Gallery Gallery is a web based software product that lets you manage your photos.
Zenphoto 1.1.4 Zenphoto is an answer to lots of calls for an online gallery solution that just makes sense.

Project Management

dotProject 2.1.1 An open source project management tool.
PHProjekt 5.2 PHProjekt is a modular application for the coordination of group activities and to share informations and document via intranet and internet.
Survey Advanced Poll 2.0.2 Advanced Poll is a polling system with powerful administration tool.
LimeSurvey 1.53 LimeSurvey is a set of PHP scripts that interact with MySQL to develop surveys, publish surveys and collect responses to surveys.

Tracker

Bugzilla 3.1.3 Bugzilla is server software designed to help you manage software development.
Flyspray 0.9.9.4 Flyspray is an uncomplicated, web-based bug tracking system for assisting with software development.
Mantis 1.1.1 Mantis is a free popular web-based bugtracking system.

Wiki

DokuWiki 06-26b DokuWiki is a standards compliant, simple to use Wiki, mainly aimed at creating documentation of any kind.
Instiki 0.12.0 Instiki is a wiki clone with strong focus on ease of installation and running.
MediaWiki 1.9.3 MediaWiki is a free Wiki software package, used to run WikiPedia.
Php-Wiki Php-WikiWeb is a web site where anyone can edit the pages through an HTML form.
TikiWiki 1.9.9 A full featured free software Wiki/CMS/Groupware written in PHP.

Others

eTicket 1.5.6 eTicket is a widely-used open source support ticket system.
osTicket 1.6.rc3 osTicket is a widely-used open source support ticket system.