DjVu is a web-centric format and software platform for distributing documents
and images. DjVu can advantageously replace PDF, PS, TIFF, JPEG, and GIF for
distributing scanned documents, digital documents, or high-resolution pictures.
DjVu content downloads faster, displays and renders faster, looks nicer on a
screen, and consume less client resources than competing formats. DjVu images
display instantly and can be smoothly zoomed and panned with no lengthy
re-rendering.

DjVuLibre is a free (GPL'ed) implementation of DjVu, including viewers,
decoders, simple encoders, and utilities. The browser plugin is in its own
separate sub-package.