XQuery is a relatively new initiative by the W3C, which is gaining popularity
despite some initial contraversy and push back from XSLT supporters.
For a brief introduction, see this XML.com article by Per Bothner:
I am actively working with Per on his Open Source Implementation - QEXO and will soon
launch a sandbox on this server. It will demonstrate XQuery's feasibility for building real world web applications easier and
faster than it used to be with previous technologies. It will also show how XQuery makes a terrific tool for orchestrating REST Web Services.