This is a wiki written in VisualWorksSmalltalk. You can downloaded it from Cincom (http://www.cincom.com/scripts/smalltalk.dll//downloads/index.ssp); it is also included in each VisualWorks package.
Some notable features of this wiki engine are an upload facility, HTML support, and support for renaming pages.
UIUC uses this wiki engine; see http://wiki.cs.uiuc.edu/VisualWorks, and also http://wiki.cs.uiuc.edu/.