The use or optional use of an external revision control system as the backend in which the versioned page database is stored.
Some open source revision control systems include rcs, cvs, svn, darcs, mercurial, and others.
A RevisionControlBackend could help with the implementation of a lot of other features:
All of these could be done by adding more revision control stuff to the WikiEngine internals, but at that point, you are writing a full-powered revision control program, so you may as well just use an existing one.
By using a distributed revision control system (DVCS – distributed version control system), there are even more possibilities:
Note that you would be able to use other tools not originally designed to work with wikis, and use shell scripts etc to do interesting things.
go through the results of the WikiMatrix search provided by AlexSchroeder and put them into this more detailed table. In spring 2007 that list contained ErfurtWiki, JaWiki, JSPWiki, KeheiWiki, MicKI, MidgardWiki, MoniWiki, PhpWiki, PodWiki, ProWiki, SubWiki, TWiki and WikiSH.
ikiwiki is doing a lot of this.
BayleShanks and ChuckAdams are interested in this.
BayleShanks, AlexSchroeder (via a post elsewhere)