The author’s own pitch is “occasionally useful but weirdly satisfying,” which is the honest order to put those in. It is a real Rust defragmenter — ext4 online, FAT offline — driving an adaptive block map that redraws as extents move, which is to say the screensaver everybody actually watched in 1997. It is alpha and says so: back up first, and give the FAT write path a disposable volume.