Best Content Management System (CMS)

Best Simple Open Source and Free Content Management Systems
Joomla -- (PHP)
Drupal -- (PHP)
Radiant CMS -- (Ruby on Rails)
CMS Made Simple -- (PHP)
Wordpress -- (PHP)
Acidcat CMS -- (ASP.NET)
Impress CMS -- (PHP)
XMLNuke -- (XML)
Nucleus CMS -- (PHP)
Movable Type -- (Perl)
b2evolution -- (PHP)
Oxite -- (ASP.NET)

Best Enterprise Content Management Systems
Open Text
eZ Publish
Bitrix
Alfresco Enterprise (Java, Open Source)
Sitecore
Dot CMS (Java)

Best Wiki Management Platforms
Media Wiki PHP, (open source)
Confluence Enterprise Wiki
JAMWiki
TiddlyWiki
DotWiki
Socialtext Workspace
TWiki
XWiki