Dr.Explain - Dr.Explain software is a help file authoring tool.
MadCap Flare - Documentation for Any Audience, Language or Format
Help & Manual - Help & Manual is a documentation authoring tool that allows you to create a single source text and convert it into a number of other target formats.
Document360 - Self-service knowledge base software focused on SaaS Products & Enterprise Software Projects.
HelpSmith - HelpSmith is a help authoring tool to create CHM HTML help files, manuals, and PDF documents.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.