Those are both interesting projects. Quilt has a rather different emphasis, though. The difference from CVMFS is that Quilt is a full set of services around data (build, push, install) whereas CVMFS is just the file system. In the big data community Paruqet, which we use as a virtualization format, has far more traction than CVMFS. Nixos is specialized for software package management so the distinctions between Quilt and git apply https://news.ycombinator.com/item?id=14772036.