What are some alternatives?
MadCap Flare - Documentation for Any Audience, Language or Format
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Dr.Explain - Dr.Explain software is a help file authoring tool.
Confluence - Confluence is content collaboration software that changes how modern teams work
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Nuclino - Nuclino is a unified real-time workspace for teams that brings all your notes, tasks, and docs together in one place.