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.
Dr.Explain - Dr.Explain software is a help file authoring tool.
Snagit - Screen Capture Software for Windows and Mac
MadCap Flare - Documentation for Any Audience, Language or Format