Blogs:
b2evolution

Nucleus

pMachine Free

WordPress

Content Management:
Drupal

Geeklog

Joomla

Mambo Open Source

PHP-Nuke

phpWCMS

phpWebSite

Post-Nuke

Siteframe

TYPO3

Xoops

Customer Support:
Crafty Syntax Live Help

Help Center Live

osTicket

PerlDesk

PHP Support Tickets

Support Logic Helpdesk

Support Services Manager

Discussion Boards:
phpBB2 (v3 any day now)

SMF

E-Commerce:
CubeCart

OS Commerce

Zen Cart

FAQ:
FAQMasterFlex

Guestbooks

ViPER Guestbook

Hosting Billing

AccountLab Plus

phpCOIN

Image Galleries:
4Images Gallery

Coppermine Photo Gallery

Gallery

Mailing List:
PHPlist

Polls and Surveys:
Advanced Poll

phpESP

PHPSurveyor

Project Management:
dotProject

PHProjekt

Site Builders

Soholaunch Pro Edition

Templates Express

Wiki:
TikiWiki

PhpWiki

Other Scripts:
Dew-NewPHPLinks

Moodle

Noahs Classifieds

Open-Realty

phpAdsNew

PHPauction

phpFormGenerator

WebCalendar