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.
wpDocs - wpDocs enables users to create step-by-step instructions with images and display them in minutes.
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
StepShot - Make knowledge sharing more time-efficient!