See alphabetical list of major XML languages and a list of XML languages by discipline/domain (both lists are Wikipedia pages that we can augment as we find other languages).
MEI (Music Encoding Initiative)
TEI (Text Encoding Initiative)
Beer XML: https://en.wikipedia.org/wiki/BeerXML
DocBook (widely used for writing and encoding technical documentation)
EPUB
KML (Keyhole Markup Language)
MARC XML
Open Office XML
