Wiki :

phpWiki   Short description: PhpWiki is a web site where anyone can edit the pages through an HTML form. Linking is done automatically on the server side; all pages are stored in a database. Disk space required to install : 0 MB

TikiWiki   Short description: TikiWiki is designed to be an international, clean and extensible Content Management System and Groupware that can be used to create all sorts of web applications, sites, portals, intranets and extranets. TikiWiki also works great as a web-based collaboration tool. TikiWiki has a lot of native options and sections that you can enable/disable as you need them. Disk space required to install : 2.8 MB