Is there a NAS-based sync app?

I have used a server-based sync app based in the cloud (Acronis TrueImage) and I liked it until it stopped working.  I could find a similar app and set it up again.  I know DropBox works well, and that is probably what I would choose.  However, I am thinking that a better solution is to have the synchronizing software reside in the NAS instead of the cloud.  By eliminating the cloud, that architecture would certainly be much faster and much more robust.  When I purchased my RN212, I misread the advertising and thought that Resilio Sync would be just that. 

Now I discovered that Resilio Sync is purely point-to-point, which would require me to have all my machines on at once to be sure the files are synced.

Does anyone know of a server-based sync app that resides in the NAS212?  I have been searching, but to no avail.

Thanks in advance.