DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
Banana Dance Wiki/CMS - Free open source software combining the best of wiki and CMS with community building-features.
Oddmuse - Oddmuse is a wiki engine.
Pepperminty Wiki - An entire wiki in a single PHP file. Intended for small - medium sized wikis.
MoinMoin - MoinMoin is an advanced, easy to use and extensible WikiEngine with a large community of users.