phplist is listed as a featured site on
http://wikkawiki.org/WikkaSites
You may have to reload that page a few times to make phplist appear, as it seems to be running from some random content system. I hope their servers can handle the demand.
We use this Wiki engine for our documentation section.
It may not be obvious but this site mixes a few different (open source of course) systems to make them all look like each other. First of all there is the above Wiki engine, which is our documentation section. Then you have the forums which run on
www.phpbb.com and the issue tracker (which we can't live without) which uses
www.mantisbugtracker.com. Then of course the information pages, which run on
www.webbler.org (oops sorry, that one's not actually open source, but it's our own CMS) and then last but not least the newsletter bits are of course handled by
www.phplist.com.
All quite tricky to make things look the same, but Bevan did a great job to pull it all together and Hernan is doing a great job to keep it all together.