What are some alternatives?
When comparing Adobe RoboHelp and Dr.Explain, you can also consider the following products
MadCap Flare - Documentation for Any Audience, Language or Format
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.
WinCHM - Creating CHM file, Make CHM file, Web Help. WinCHM Pro - Help authoring software (CHM, WebHelp, DOC, PDF) . With this powerful tool you can not only create chm file from scratch, but also convert a set of existing HTML files to a chm file.
Manula - Manula is an online software for creating user manuals.
CHM Editor - Best solution to edit CHM files