XUP is an attempt to replace static per-site user accounts, which most present dynamic web sites use in absence of an easy to use and open/shared user account system. It allows people to use a single account or profile with many sites, or one of their existing user profiles on multiple other web sites.
This document describes a horribly simple but flexible XML format which holds user account information for reuse by different web sites and applications.
Though both follow different goals, this format halfway competes with FOAF.
As said earlier, the XML User Profile format is simple, and not RDF based.
Only just found this. Actually seems harder to understand than FOAF to me.