Okular - Okular is a universal document viewer based developed by KDE.
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.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Kchmviewer - Kchmviewer is a free, open-source CHM (MS HTML help) and EPUB viewer for Unix, Mac and Windows...
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
Microsoft HTML Help - Microsoft HTML Help is the standard help system for the Windows platform.