Kchmviewer is a handy open source viewer for CHM (Compiled HTML Help) files, a common format used for software documentation. It has more features than Microsoft's own viewer, does a better job of supporting non-English CHMs, and can display EPUB files, too.

The core of the program works much like the standard viewer, so you'll be using it right away. A Contents tree displays the file's folders and pages; clicking one of these displays it in the viewing window, and there's a Search box to locate the text you need.

Kchmviewer also includes a bookmarking system, though, allowing you to save important places on any page and quickly recall them later.

A simple tabbed interface means you can have several pages open simultaneously.

You're able to increase or decrease the font size on any page, an easy way to zoom in or out.

There are bonus options to display the HTML source of the current page, or extract the entire contents of a CHM file.

Kchmviewer can also open EPUB files. It refused to display one of ours, for no apparent reason, but successfully rendered everything else.