HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Helppier - Helppier provides tools to create interactive user guides in minutes.
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Dozuki - Dozuki is a web-based tool for creating and distributing step-by-step documentation.
MadCap Flare - Documentation for Any Audience, Language or Format