MadCap Flare - Documentation for Any Audience, Language or Format
MkDocs - Project documentation with Markdown.
ClickHelp - Create, translate, and publish technical documentation easily in one portal, anywhere in the world!
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Docusaurus - Easy to maintain open source documentation websites