Discussion Boards:
phpBB2
SMF

Blogs:
b2evolution
Nucleus
WordPress

Portals/CMS:
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

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:
PHProjekt
dotProject

Site Builders:
Soholaunch Pro Edition
Templates Express

Wiki:
PhpWiki
TikiWiki

Other Scripts:
Dew-NewPHPLinks
Moodle
Noahs Classifieds
Open-Realty
phpAdsNew
PHPauction
phpFormGenerator
WebCalendar