Dr.Explain - Dr.Explain software is a help file authoring tool.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
MadCap Flare - Documentation for Any Audience, Language or Format
Manula - Manula is an online software for creating user manuals.
HelpScribble - HelpScribble is a full-featured help authoring tool for easily creating professional Windows help files from start to finish.
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.