Shake is a defragmenter that runs in userspace, without the need of patching the kernel and while the systems is used. There is nothing magic in that: it just works by rewriting fragmented files. But it has some heuristics that could make it more efficient than other tools, including defrag and, maybe, xfs_fsr.
This is a companion discussion topic for the original entry at https://copr.fedorainfracloud.org/coprs/swg/shake/