MadCap Flare - Documentation for Any Audience, Language or Format
Dr.Explain - Dr.Explain software is a help file authoring tool.
Document360 - Self-service knowledge base software focused on SaaS Products & Enterprise Software Projects.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
Adobe RoboHelp - Adobe RoboHelp empowers organizations to deliver engaging help and policy content across mobile devices, formats, and platforms.
ClickHelp - Author, host and deliver docs across platforms and devices