Some Wiki Clones:
Wiki engines using different forms
Wiki Engines XWiki is a Wiki Wiki clone written in Java which supports many popular features of other Wikis
www.xwiki.org 
Twiki
a flexible, powerful, and easy to use Enterprise Collaboration Platform
Description
(GPL Perl CGI)
Targets the corporate intranet world
TWiki fosters information flow within an organization
lets distributed teams work together seamlessly and productively
eliminates the one-webmaster syndrome of outdated intranet content
Foswiki
a fork of TWiki
Didi Wiki is tiny Wiki server written in C.
Dir Dir a minimalist Wiki written in Rc Shell and using the tools in Plan Nine From User Space.
Free Wiki hosting:
AtWiki
Description
[@Wiki - free rental wiki service?](free alpha account available)
JotWiki
Description
(free beta account available)
Wikidot
Description
free "Web 2.0" social wiki hosting + forums Wi'kispaces
Description
(free accounts and supports tables) bluwiki
Description
community maintained wiki with one namespace, diverse content Wikia
Description www.compozt.com
Large Wiki provider, founded by Jimmy Wales (Wiki Pedia Founder) and Angela Beasley
Orain
Description
Wiki farm using Media Wiki. Founded in 2013. Relatively small.
More links:
Article on Wiki as Do-it-yourself software
www.businessweek.com
Flexwiki Introduction
www.flexwiki.com (by a MS project manager)
Download it
www.flexwiki.com
Ruby wiki called Instiki
instiki.org (Ruby)
Download it
Description
Instiki is a Wiki Clone that's so easy to set up and so pretty to look at
you'll be wondering whether this is a real wiki at all."
See original on c2.com