Eliot Kimber - Adobe MARS: Looks Interesting:

"MARS is an XML-based format that is intended as a functional replacement for PDF. It's not really accurate to call it an XML version of PDF because it's not a simple transliteration of PDF into tags (which could be done easily enough) but a ground-up exercise in designing and XML-based scheme for doing what PDF does.

[...] MARS tries to use standards as much as it can and it seems to do so to a remarkable level of completeness. It uses SVG for representing each page, supports the usual standards for media objects (bitmaps, videos, etc.). Uses Zip for packaging, and so on."