TikiWiki is one of the many open-source applications available for building wiki's.
TikiWiki is one of the PHP-based wiki's, but it is most interesting because the developers are trying to make it into a comprehensive CMS application.
TikiWiki provides the ability to include all of these features in your web site:
- Wikis (like Wikipedia)
- Forums (like phpBB)
- Blogs (like WordPress)
- Articles (like Digg)
- Image Gallery (like Flickr)
- Map Server (like Google Maps)
- Link Directory (like DMOZ)
- Multilingual (like Babel Fish)
- Bug tracker (like Bugzilla)
- RSS feeds (in & out)
- Free source software (LGPL)
You could install TikiWiki and have all this -- with only one management interface.
I have one TikiWiki instance installed, but that project is on hold. I will probably be working with this more in the future.
Some good resources on wiki software: