Editthis - A free wikifarm project allowing to keep private wiki and build it up through MediaWiki syntax.
Fandom - The entertainment site where fans come first.
SaidIt.net - Saidit.net - say your truth.
Miraheze - Miraheze is a wiki farm (hosts wikis) for free and with no ads, it also provides custom domains...
Wikidot - Online collaborative wiki hosting for organizations,etc.
Wikiful - Wikiful is an online platform that makes it easy to build and share a wiki.