DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
BlankPage - Stay motivated to write, and finish your story
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
Novelize - Novelize is an online novel writing app designed to keep authors on track.
TiddlyWiki - a non-linear personal web notebook
Manuskript - Open-source tool for writers.