xchm - xCHM is a cross-platform GUI front-end to chmlib, with borrowed bits from Pabs' chmdeco project.
Chmox - Chmox is a free (of charge), open source application for OS X which lets you read Windows Help...
Microsoft HTML Help - Microsoft HTML Help is the standard help system for the Windows platform.
CHM Editor - Best solution to edit CHM files
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.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.