Portals/CMS:
Drupal  
Geeklog
Joomla 1.5 
Joomla  
Mambo Open Source  
PHP-Nuke  
phpWCMS  
phpWebSite  
Post-Nuke  
Siteframe  
Typo3  
Xoops 

Customer Support:
Crafty Syntax Live Help  
Help Center Live  
osTicket  
PerlDesk  (Commercial, needs license) 
PHP Support Tickets 
Support Logic Helpdesk 
Support Services Manager  

Discussion Boards:
phpBB 
SMF  

E-Commerce:
CubeCart 
OS Commerce (Candidate 2a + buySAFE) 
Zen Cart  

FAQ:
FAQMasterFlex 

Guestbooks:
 (X1.1) 

Hosting Billing:
AccountLab Plus (Commercial, needs license) 
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  (Commercial, needs license) 
Templates Express 

Wiki:
PhpWiki
TikiWiki 

Other Scripts:
Dew-NewPHPLinks
Moodle 
Noah’s Classifieds 
Open-Realty 
phpAdsNew 
PHPauction 
phpFormGenerator 
WebCalendar