[Update] XMLQuire was originally recommended in this answer. It was a free XML editor for Windows with the SketchPath XPath Editor built in for XPath testing.
XMLQuire has not been maintained for a few years and has now been retired.
For XPath experimentation etc. XMLQuire’s author now recommends the XPath Notebook extension for Visual Studio Code. Developed by the same author, this now supports XPath 3.1 courtesy of Saxonica’s Saxon-JS processor.
