• Installed for testing on HomeBizNizz.net
  • Content Management Systems (Wikipedia)(OpenSourceCMS list)(Wikipedia list)
    • Pligg (Website)(Demo at OpenSourceCMS)
    • phpMySport (Website)(Demo at OpenSourceCMS)
    • PHP-Fusion (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • Mambo (Website)(Wikipedia)(Demo at OpenSourceCMS)(Demo)
    • Mambo Lite (Website)(Wikipedia)
    • MiaCMS (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • MiaCMS Lite (Website)(Wikipedia)
    • Dragonfly CMS (Website)(Wikipedia)
    • e107 (Website)(Demo at OpenSourceCMS)
    • Drupal 5x (Website)(Wikipedia)
    • Drupal 6x (Website)(Wikipedia)(Demo at OpenSourceCMS)
  • Blogs (Wikipedia)(OpenSourceCMS list)
    • FlatPress (Website)(Demo at OpenSourceCMS)
    • b2evolution (Website)(Wikipedia)
  • Forums (Wikipedia)(OpenSourceCMS list)
    • PunBB (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • MyBB (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • phpBB (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • Phorum (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • Simple Machine Forum (Website)(Wikipedia)(Demo at OpenSourceCMS)
  • Webshops (OpenSourceCMS list)
    • ZenCart (Website)(Wikipedia)(Demo at OpenSourceCMS)
    • CubeCart (Website)(Wikipedia)
  • Wikis (Wikipedia)(OpenSourceCMS list)
    • Mediawiki (Website)(Wikipedia)
  • Other
    • Name (Website)(Wikipedia)(Demo at OpenSourceCMS)

Go here for a huge list with opensource PHP-scripts.
You can even try them out too.