The CHM files (Microsoft compiled HTML help files) are often used for eBooks. They are readable on OS-X using excellent open source CHMOX application. If you want to get more useful preview in OuickView than the not very helpfull static icon, get this plugin.
How to install it: Unzip it, take the proper package for your system (the ZIP file contains several architectures, on modern Intel-based Mac's you want to use x64), put it inside
and enjoy !
Big thanks to the developer Qian Qian - whoever that is.