xCHM is a program for reading Compiled HTML files that lots of Windows programs use for Help files. Also lots of e-books and other documentation comes in this format (such as the Java class library docs and the PHP docs.) Previously, there was no way to open these on a Mac without using a utility to decompress them into a million tiny .html files and read them in a browser.
This is a binary for the xCHM open source program which was originally written for Linux. Thanks to the fact that it was written using wxWindows, it was fairly easy to compile to run natively on OS X. I just tweaked the code to make it a bit more Mac friendly, and created an easily double-clickable application bundle for it. It still has some un-Mac like warts, but it works pretty well. I plan on trying to fix some of the problems and submit my changes back to the original developer.
Note that X11 is NOT required. This program runs natively (well, it's Carbon.)