clsync is described as 'This utility has been written for two purposes: for making high availability clusters; for making backups of them; consider it a better and faster lsyncd written in C' and is an app in the Backup & Sync category. There are three alternatives to clsync for a variety of platforms, including Linux, Mac, Windows, BSD and Cygwin. The best alternative is rsync, which is both free and Open Source. Other great apps like clsync are Unison (Free, Open Source) and lsyncd (Free, Open Source).
Lsyncd watches a local directory trees event monitor interface (inotify or fsevents). It aggregates and combines events for a few seconds and then spawns one (or more) process(es) to synchronize the changes. By default this is rsync.