HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Dr.Explain - Dr.Explain software is a help file authoring tool.
Wiki.js - An open source, modern and powerful wiki app built on Node.js, Git, and Markdown.
CHM Editor - Best solution to edit CHM files
TiddlyWiki - a non-linear personal web notebook