DjVu needs only half the size than jpg images for photos of the same quality and displays photos of the same size in a higher better quality. Look at the comparison between jpg and djvu images, very interesting and a file format to look out for.

It’s one of the favorite formats for technical documentations and scientific documents. The viewer itself is a no thrills no frills viewer that can display the supported formats. It was designed with speed in mind, it opens pdf documents as fast, or even a bit faster, than Foxit Reader which is one of the fastest of its kind.

The main benefit of STDU Viewer is the support of the three mentioned formats and its speed. There is not really a reason to change from Foxit Reader to it if you only work with pdf documents on your system. If you use at least two of the formats it might be a viable alternative.

The official djvu website has a download section with additional clients for Windows, Mac and Linux plus an add-on for Microsoft Office.