MediaWiki

https://github.com/wikimedia/mediawiki
This is the software behind Wikipedia and is a popular, open-source wiki software. It's highly customizable and has a large community of users and developers.
SVL: PHP might be needed

Confluence

https://www.atlassian.com/software/confluence
Offered by Atlassian, Confluence is a professional wiki and team collaboration tool. It integrates well with Jira and other Atlassian products and is suited for both small teams and large enterprises.

Wikidot

https://www.wikidot.com/
This is an easy-to-use wiki hosting service that offers free and paid plans. It's versatile and can be used for creating a variety of sites, from personal notes to large community websites.

DokuWiki

https://www.dokuwiki.org/dokuwiki
A simple to use and highly versatile open-source wiki software that doesn't require a database. It's known for its clean and readable syntax.

TiddlyWiki

https://tiddlywiki.com/
A unique non-linear notebook for capturing, organizing, and sharing complex information. It's a single HTML file that you can store anywhere.

Fandom

https://www.fandom.com/
(previously known as Wikia): A hosting service and domain for wikis (known as "wikis") on various subjects, from pop culture to literature. It's more for community and fan-based content.

PBworks

https://www.pbworks.com/
This is a commercial, feature-rich option for business and educational wikis. It offers tools for team collaboration, project management, and document management.

Miraheze

https://miraheze.org/
A community-centric, ad-free, and free-to-use wiki hosting service

MediaWiki

https://www.mediawiki.org/wiki/MediaWiki
It's maintained by volunteers and funded by donations.

Notion

https://www.notion.so/
While not a traditional wiki, Notion offers a set of tools for note-taking, data management, project management, and knowledge repository that can function effectively as a modern wiki for teams and individuals.

Credit for research to Steven Van Loon of www.VirtualWorlds.Museum