HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Dr.Explain - Dr.Explain software is a help file authoring tool.
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
Manula - Manula is an online software for creating user manuals.
Doc-O-Matic - Doc-O-Matic is a software source code documentation and Help authoring tool.