UniSync is an open-source File synchronization program for Linux and Windows. It is an open source utility for efficiently comparing or synchronizing large directory structures by checking names and sizes or optionally the times or even the contents by hashes. (Md5 or Sha-2) The UniSync can even synchronize offline directories (Which are not available same time) by creating a catalog file and making and update package according to that.
The UniSync has a graphical user interface names UniSyncGui. https://github.com/hyper-prog/unisyncgui
Compile / Install
Simply rename Makefile.linux to Makefile and hit "make" to compile it.