ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Rulingo - Translation workflow automation solution
Natural Docs - Natural Docs is an open-source documentation generator for multiple programming languages.
SDL Trados Studio - SDL Trados Studio is the complete translation environment for language professionals who want to edit, review and manage translation projects.
Doxygen - Generate documentation from source code