GML (Geographic Markup Language) is an industry-standard XML format for expressing vector geometries and their attributes. GML is readable by a variety of different F/OSS GIS packages, most notably any that depend on the OGR library, including QGIS and GRASS GIS.
Converting OSM XML
- OGR tools (such as ogr2ogr) support GML and (more recently) OSM XML as an in-built thing. Allowing you to covert between these formats. Many tools bundle OGR functionality too, so tools such Osmium and QGIS naturally support this conversion too.
- progserega offers a more specific tool on github: https://github.com/progserega/gml2osm written in C. Not very well documented though
Quite early on the project's history we were able to convert OSM XML into GML using two different approaches developed by User:Crschmidt and User:SchuylerErle. Both methods however were not updated to work with OSM XML format updates (old API version 0.5) and so the above method are recommended.