What are some alternatives?
When comparing KEL CHM Creator and HelpNDoc, you can also consider the following products
Chmox - Chmox is a free (of charge), open source application for OS X which lets you read Windows Help...
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.
CHM Editor - Best solution to edit CHM files
Helpinator - WYSIWYG, single source, multiformat, multilingual help authoring tool with screenshot capture and annotation. CHM, PDF, WebHelp, QtHelp, JavaHelp, OracleHelp, WordPress. 249USD.
MadCap Flare - Documentation for Any Audience, Language or Format
Microsoft HTML Help - Microsoft HTML Help is the standard help system for the Windows platform.