Perl-based Wikis

CorneliOS, a webOS, includes a wiki software that`s also the engine for Galaxiki.

Noösphere, the engine for PlanetMath.

PodWiki is a wiki which supports multiple markup languages, primarily Perl POD.

Socialtext is an enterprise wiki and weblog partially derived from open-source Kwiki. Socialtext is available as a hosted service, a dedicated hardware appliance, or as free downloadable open-source software (and a VMware virtual appliance) from Sourceforge.

TWiki is a structured wiki, typically used to run a project development space, a document management system, a knowledge base, or any other groupware tool. Also available as a VMware appliance.

UseModWiki (Clifford Adams, 2000) is a clone of AtisWiki.

Oddmuse is a fork of UseModWiki.

PurpleWiki is major rewrite of UseModWiki that implements Purple Numbers and Transclusion.

WikiWikiWeb (Ward Cunningham, 1994)

QuickyWiki (Ward Cunningham, from his book "The Wiki Way") is a minimalist Wiki implementation that works (open source).

While not strictly Wiki software, weblog-engine Blosxom mostly meets the definition when used with its wikieditish and wikiwordish plugins. There are also plugins available that enable Blosxom to use the text parsers from Kwiki, TWiki, or PurpleWiki.