JSON Proxy is an App Engine app that will fetch a publicly accessible XML document, transform it to JSON, and return it. The proxy is a simple GET form, so JavaScript users can generate URLs to be able to fetch otherwise inaccessible XML across domains.

Home page here: http://jsonproxy.appspot.com/

About: http://jsonproxy.appspot.com/about

Examples: http://jsonproxy.appspot.com/examples