kchmviewer is a viewer for Windows HTML compressed help (CHM) and Ebook (EPUB) files. It's either buildable as KDE application or standalone Qt program. It has broad support for internationalized charsets and help files.
TEBookConverter is an easy to use ebook converter for Windows. It utilizes Calibre. Supported input formats therefore are cbz, cbr, cbc, chm, djvu, docx, epub, fb2, html, htmlz, lit, lrf, mobi, odt, pdf, prc, pdb, pml, rb, rtf, snb, tcr, txt, txtz. Supported output formats are azw3, epub, fb2, oeb, lit, lrf, mobi, htmlz, pdb, pml, rb, pdf, rtf, snb, tcr, txt, txtz. It provides a speedy conversion process due to being multi-threaded.