Miraheze - Miraheze is a wiki farm (hosts wikis) for free and with no ads, it also provides custom domains...
Litnerd - The Pixar for education, reading program for K-5 schools
Investopedia - Investopedia has a lot of information to share with business mind people.
Cotrio - The most beautiful way to move your brain and imagination
Editthis - A free wikifarm project allowing to keep private wiki and build it up through MediaWiki syntax.
WonderBox - Wikipedia for kids — Learn with friends and family