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.
Dr.Explain - Dr.Explain software is a help file authoring tool.
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
snazzyDocs - Publish and Host your documentation in seconds!
Innovasys HelpStudio - Help Authoring Made Easy.