It is simple host-client file synchronizer like rsync. It's purposed to sync files between host and docker-machine in dev process.
Rsync works well, but it's not meant to quick update changes. After file change detect, rsync is rescanning whole tree and compares every file modifed date with client's version. It consumes a lot of time, so changes are delayad even few seconds after save file.
This is not acceptable in during dev process.
flysync uses chokidar package on host. Depending on file system, cahnge detecting time are different. flysync update only
changed files. It doesnt rescan whole tree. Also, it keeps client connection open, so there is no ping effect.
Most of time delay is not noticable.