kchmviewer is a viewer for Windows HTML compressed help (CHM) and Ebook (EPUB)
It's either buildable as KDE application or standalone Qt program.
It has broad support for internationalized charsets and help files.
7.113 Oct 2014 21:55
Added support for portable applications.
Fixed a crash when parsed entity was empty.
Fixed parsing CHM files whose filenames contained URL-encoded symbols.
Added images to EPUB TOC.