Wikis can also be created on a "wiki farm", where the server side software is implemented by the wiki farm owner. PBwiki, Socialtext, Wetpaint, and Wikia are popular examples of such services. Some wiki farms can also make private, password-protected wikis. Note that free wiki farms generally contain advertising on every page. For more information, see Comparison of wiki farms.
Read more about this topic: Wikisphere