What are some alternatives?
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.
MadCap Flare - Documentation for Any Audience, Language or Format
Airim - Show personalised FAQs before live chat
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Doc-O-Matic - Doc-O-Matic is a software source code documentation and Help authoring tool.
Doxter - Software for creating, organizing and publishing project documentation