Based on its name I think it's used in Arch Linux packages (at least makepkg say...

		themulticaster on Sept 27, 2023 \| parent \| context \| favorite \| on: Introduction to sysclean(8) Based on its name I think it's used in Arch Linux packages (at least makepkg says it is generating an mtree file at some point during the build process IIRC). However it appears mtree (the tool) isn't packages, so perhaps it's only using the mtree specification format?