DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Tiki Wiki CMS Groupware - Tiki Wiki CMS Groupware, also known as Tiki (or TikiWiki), is a full-featured, web-based, multilingual, all-in-one Free/Libre Open Source Software solution. Tiki can be used to create all kinds of web apps, portals, knowledge bases, intranets, etc.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
TiddlyWiki - a non-linear personal web notebook
MDwiki - Static single file CMS/Wiki done purely with client-side Javascript and HTML5.
XWiki - A powerful Open Source collaborative platform enhancing collaboration and communication.