TreeStages has released
XEntrant 0.2, a closed source, Windows "Model Driven XML Tree Editor" that supports W3C schemas and XSLT. Pricing does not seem to be available.
XEntrant is written in Python and seems to make the same mistake 90% of XML editors have made over the last ten years; specifically the user interface is designed according to what the program's developers find easy to code rather than what the program's users would find easy to code in. Tree-based editors just aren't all that useful, but they're relatively easy to develop. Linear editors are much more useful, but they're also much harder to write.
