X Steps Recorder - A clone of Microsoft's Problem Steps Recorder, but for linux.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Folge - The fastest tool for creating step-by-step guides.
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
Snagit - Screen Capture Software for Windows and Mac
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.