SketchPath will be freeware and includes many features required of a
stand-alone XPath tool for development and re-use of XPath against
sample XML.

Features include: namespace/variable management, colorization of
XPath, predicate-aware auto-completion, XPath auto-generation,
compressed-xml support and predicate 'step-into' debugging.

Currently limited to .NET version of XPath 1.0, but - if there's
interest - hoping to gradually extend this for Saxon.NET / XPath 2.0.
(I might have quite a few questions on this later)

More details and early Beta download at:
http://www.sketchpath.com