GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
MkDocs - Project documentation with Markdown.
Docusaurus - Easy to maintain open source documentation websites
DocFX - A documentation generation tool for API reference and Markdown files!
Archivy - A self-hosted knowledge repository that allows you to safely preserve useful content that contributes to your own personal, searchable and extensible wiki.
Slate API Docs Generator - Create beautiful, intelligent, responsive API documentation.