The Wikimedia Foundation and its sites are strictly non-commercial, with a mission to spread knowledge under free licences. But if you wanted a personal wiki, or one targeting a specific niche or industry, you could create one on Wikia, the commercial offshot also co-created by Jimmy Wales.
I didn’t like their heavy UI changes. For example, the self-hosted Grand Order Wiki, and the late Whole Wheat Radio, benefit and benefited from being closer to stock MediaWiki. But Wikia was still usable enough to develop an ecosystem of wikis, and reached critical mass with editors.
In 2016 Wikia was renamed Fandom, owing to a preponderence of its wikis being fansites. But the URL remained wikia.com, so sites for topics like cancer support would still be respectful and make sense.
I missed this back in August, but as part of their continuing rebrand the site will be redirecting to fandom.com in 2019. This seems misguided, for the reason stated above. The comment thread on the announcement is eleven pages long, with people saying as much.
Legally, Fandom have every right to change their site. But it doesn’t seem respectful to all those people who poured their hearts and time into their sites, and thereby ensuring their commercial success.