Comic book archives (.cbr or .cbz) are files containing comics. Internally these are compressed folders (using zip or rar, and changing the extension of the compressed file) containing images. This allows you to keep the group of images together in one handy format, without running the risk of loosing some pages.
Version 0.9.4 Just got released. Still in beta but there are a few improvements:
Version 0.9.3 is now available. As you can see from the version number it is still in beta. There is 1 known issue: when opening a file, the firs page is automatically displayed, in 50% of the cases, the main image is corrupted. However going forward and back again shows the correct image. The thumbnail is also always correct.
I'm still investigating what is going on, but you can download the version already if you wish. Download here.