xps files
XPS is a Microsoft document standard, which stands for “XML Paper Specification“. It is basically a zipped XML file. Under Linux you can open it with okular.
Windows Vista includes it by default, and uses it as the spooler format (Linux uses Postscript, and there’s a move to switch to PDF), and uses IE as the viewer. WinXP users get it through .NET 3.0
From the Wikipedia article, the XPS standard is released by M$ “under a royalty-free patent license“, however “as long as you include a notice within the source that technologies implemented may be encumbered by patents held by Microsoft“. Hmm, that doesn’t sound too nice :-/
Reference: http://en.wikipedia.org/wiki/XML_Paper_Specification

Related Launchpad bug and Brainstorm idea to add .xps support to evince:
https://bugs.launchpad.net/ubuntu/+source/evince/+bug/114462
http://brainstorm.ubuntu.com/idea/12700/