xchm - xCHM is a cross-platform GUI front-end to chmlib, with borrowed bits from Pabs' chmdeco project.
Microsoft HTML Help - Microsoft HTML Help is the standard help system for the Windows platform.
Chmox - Chmox is a free (of charge), open source application for OS X which lets you read Windows Help...
Read CHM - Read CHM is ultimate CHM (Compiled HTML Help) file reader.
CHM Editor - Best solution to edit CHM files
CHM Reader Pro - CHM Reader Pro is can read CHM file and Convert CHM to PDF.