Blogs:
b2
b2evolution
Nucleus
pMachine Free
WordPress

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

Customer Support:
Crafty Syntax Live Help
Help Center Live
osTicket
PHP Support Tickets
Support Logic Helpdesk
Support Services Manager

Discussion Boards:
Invision Board
phpBB2
YaBBSE

E-Commerce:
CubeCart
OS Commerce

FAQ:
FAQMasterFlex

Image Galleries:
4images Gallery
Coppermine Photo Gallery
Gallery

Mailing List:
PHPlist

Polls and Surveys:
Advanced Poll
phpESP
PHPSurveyor

Project Management:
PHProjekt
dotProject

Wiki:
PhpWiki
TikiWiki

Other Scripts:
Moodle
Noah’s Classifieds
Open-Realty
phpAdsNew
PHPauction
phpCOIN
phpFormGenerator
phpLinks
WebCalendar