Blogs:
b2evolution (website)
Nucleus (website)
WordPress (website)

Classifieds:
Noah’s Classifieds (website)

Portals/CMS:
Drupal (website)
Geeklog (website)
Joomla (website)
Mambo Open Source (website)
phpWCMS (website)
phpWebSite (website)
Post-Nuke (visit site)
Siteframe (website)
Typo3 (website)
Xoops (website)

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

Discussion Boards:
phpBB (website)
SMF (website)

E-Commerce:
CubeCart (website)
OS Commerce (website)
Zen Cart (website)

FAQ:
FAQMasterFlex (website)

Hosting Billing:
AccountLab Plus (Commercial, needs license) (website)
phpCOIN (website)

Image Galleries:
4images Gallery (website)
Coppermine (website)
Gallery (website)

Mailing List:
PHPlist (website)

Polls and Surveys:
Advanced Poll (website)
LimeSurvey (website)
phpESP (website)

Project Management:
PHProjekt (website)
dotProject (website)

Site Builders:
Soholaunch Pro Edition (Commercial, needs license) (website)
Templates Express (website)

Wiki:
PhpWiki (website)
TikiWiki (website)

Other Scripts:
Dew-NewPHPLinks (website)
Moodle (website)
Open-Realty (website)
phpAdsNew (website)
PHPauction (website)
phpFormGenerator (website)
WebCalendar (website)