Files in DjVu format may now be uploaded to Wiki*edia. For now there is no inline rendering (eg thumbnails), so it's only really suitable for archival data such as the scans of books that go into Wikisource.
DjVu is a compressed image file format targeted at electronic versions of documents, including multi-page and machine-readable text support. As an open format which handles scanned documents better than PDF, it's used for a number of online library projects and similar. For more background, please see: http://en.wikipedia.org/wiki/DjVu
Files are checked for validity on upload, and the pixel resolution of the first page is recorded as the file's size. (See DjVuImage.php for implementation. As with SVG, you still have to whitelist the .djvu extension manually on third- party MediaWiki installations and make sure your web server is configured to serve the proper MIME type, image/vnd.djvu.)
-- brion vibber (brion @ pobox.com)