Ahhhh, now here's some cool news. FlexWiki is being released to shared source. From David Orenstein's blog:

FlexWiki posted to SourceForge.net* *

This evening FlexWiki took the next step in its life and has been made available at SourceForge.net under the Common Public License. With this step, the developer community will have the latest source (including all the WikiTalk features), better access, better tools, and a better legal environment.  The FlexWiki developer community has kinda stalled out a bit over the past few months as I've worked to get FlexWiki to this point.  Now we can really get going again!

FlexWiki is based on WikiWiki, and has a lot of nifty features.