Here are websites where you can get various versions of the DejaVu viewer.
(Copy and paste into your browser's address bar)

Windows and MAc viewers are provided by LizardTech, the developers of the DejaVu format:
http://www.lizardtech.com/

For Unix OS's viewers are available from an Open Source project:
http://djvu.sourceforge.net/

For many Linux distros DJVU cana be installed via the packaging system.