Hydrogen Audio is an audio-enthusiast's community who maintains a ZwikiClone variant at http://doc.hydrogenaudio.org/wikis/hydrogenaudio/FrontPage
It is particularly notable as they appear to have customized it quite a bit. It has features like:
- Excellent UI improvements using Javascript
- Threaded comments at bottom of pages
- Supports both TextFormattingRules and StructuredText
The link is broken and there is a link to a MediaWiki-based wiki from the main page. Did it get replaced?