MkDocs - Project documentation with Markdown.
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Docusaurus - Easy to maintain open source documentation websites
Hyperbook - Hyperbook is a quick and easy way to build interactive workbooks, that support modern standards and runs superfast.
Archivy - A self-hosted knowledge repository that allows you to safely preserve useful content that contributes to your own personal, searchable and extensible wiki.
Doxygen - Generate documentation from source code