What are some alternatives?
Dr.Explain - Dr.Explain software is a help file authoring tool.
Readymag - Readymag is a comprehensive solution that allows you to design web publication, magazines, presentations, websites, and all the other publications.
Confluence - Confluence is content collaboration software that changes how modern teams work
MadCap Flare - Documentation for Any Audience, Language or Format
Nuclino - Nuclino is a unified real-time workspace for teams that brings all your notes, tasks, and docs together in one place.
Zmags - Zmags provides solutions create and publish web experiences instantly.