GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
Sphinx Search - Sphinx is an open source full text search server, designed with performance, relevance (search quality), and integration simplicity in mind. Sphinx lets you either batch index and search data stored in files, an SQL database, NoSQL storage.
Doxygen - Doxygen is a tool for generating documentation from annotated C++ sources, as well as other popular...
Docusaurus - Easy to maintain open source documentation websites
Hugo - Hugo is a general-purpose website framework for generating static web pages.