Tiki Wiki CMS Groupware

Tiki Wiki CMS Groupware is a full-featured, tightly integrated, open source, multilingual (35+ languages), all-in-one Wiki+CMS+Groupware, written in PHP and actively developed by a very large international community. Major features include articles, forums, newsletters, blogs, file and image galleries, wiki, bug and issue trackers (form generator), calendar, RSS feeds, category system, tags, advanced permission system for users and groups, and more.

More about the semantic feature: http://doc.tikiwiki.org/Semantic