NDoc
Doxygen
Natural Docs
DocFX
Daux.io
Docsify.js
Outline Wiki
Docpress
Folderit
Help & Manual
Dr.Explain
HelpSmith
snazzyDocs
Webworks ePublisher
HelpScribble
WinCHM
NDoc
FolderitDoxygen - Generate documentation from source code
Help & Manual - Help & Manual is a documentation authoring tool that allows you to create a single source text and convert it into a number of other target formats.
Natural Docs - Natural Docs is an open-source documentation generator for multiple programming languages.
Dr.Explain - Dr.Explain software is a help file authoring tool.
DocFX - A documentation generation tool for API reference and Markdown files!
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.