Verbose, strict, and still holding up enormous amounts of the world - government feeds, financial messaging, publishing, office documents. JSON took the web from it, but anywhere with schemas and validators and twenty years of history, XML is what's on the wire.
Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop a XML file above and choose afterwards.