AquaQuery

AquaQuery is a free Cocoa-based developer tool for Mac OS X Tiger that serves as a basic XQuery authoring/debugging tool.

AquaQuery is based on Apple's excellent NSXML and WebKit toolkits. XQuery support is provided, of course, by NSXML.
Usage is simple and straightforward. Compose or paste your XML source document in the "Source" tab. Compose your XQuery in the "Query" tab.