Martin Piskernigs format ScoreML is an XML application. It isn't available online any more, but there is a plan to relaunch it as part of an open source project . He announced to use some ideas from MusiXML .
Feedback (questions, suggestions, broken links): ScoreML
My new eBook (in German)
Professionell Ankern - vom NLP-Practitioner bis zum Coaching and its Website