Dr.Explain - Dr.Explain software is a help file authoring tool.
MkDocs - Project documentation with Markdown.
WinCHM - Creating CHM file, Make CHM file, Web Help. WinCHM Pro - Help authoring software (CHM, WebHelp, DOC, PDF) . With this powerful tool you can not only create chm file from scratch, but also convert a set of existing HTML files to a chm file.
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Document360 - Self-service knowledge base software focused on SaaS Products & Enterprise Software Projects.
Docusaurus - Easy to maintain open source documentation websites