(Google and Alexa results from 14 Aug 2006) 
To every therm we added "wiki", eg. "MediaWiki wiki", "MoinMoin wiki" in an effort to exclude abiguous terms.

%%sortable
||#||__Wiki Engine__||__Google Res__||__Alexa Rank__||__License__||__Link__
|1|MediaWiki|295000000|9091|GPL2|[markup|http://meta.wikimedia.org/wiki/MediaWiki_User's_Guide:_Editing_overview]
|2|Twiki|4680000|22998|GPL
|3|TikiWiki|4130000|21130|LGPL
|4|PukiWiki|2510000|4850280|GPL2
|5|MoinMoin|2120000|58494|GPL
|6|PmWiki|1260000|31888|GPL
|7|DokuWiki|969000|556859|GPL2
|8|PhpWiki|913000|1398912|GPL
|9|MoniWiki*|861000|0|GPL
|10|TiddlyWiki|831000|92717|BSD
|11|JSPWiki|703000|92813|LGPL
|12|SnipSnap|580000|128718|GPL
|13|WackoWiki|369000|172554|BSD
|14|Xwiki|343000|184037|LGPL
|15|UseMod|282000|87300|GPL
|16|Midgard Wiki*|230000|89949|LGPL
|17|FlexWiki|220000|167955|CPL
|18|Instiki|216000|140083|GPL
|19|Zwiki|209000|174086|GPL
|20|TracWiki*|206000|87279|Mod. BSD
%%

 * Engine does not have its own domain name, so Alexa rank for this wiki is misleading.

!! Commercial Wiki Engine Popularity
(Google and Alexa results from 14 Aug 2006)

%%sortable
||#||__Wiki Engine__||__Google Res__||__Alexa Rank__||__Markup__
|1|Confluence|4580000|8652|Yes
|2|JotSpot|2300000|4850|No
|3|PBwiki|1920000|5205|Yes
|4|Socialtext|993000|50754|Yes
|5|SamePage|422000|405443|No
|6|Wetpaint|257000|10987|No
|7|Wikispaces|227000|13200|Yes
|8|SeedWiki|164000|20878|No
|9|EditMe|110000|43845|No
|10|StikiPad|109000|33897|Yes
%%