You can map a SharePoint location as a drive letter quite simply.
For example from a Windows computer:
1) Press Windows key and type CMD (select to run command prompt)
2) In the Command Prompt window, you can map a drive letter using the following command:
NET USE * http://sharepoint.server.com/site/library
This will map an available drive letter to the SharePoint site or library referenced by the URL.
Type NET USE /? if you wish to see other mapping options. For example you may want to include account credentials, and you may wish to include /PERSISTENT:YES which would ensure that this drive mapping persists over machine reboot.
You can then use any synchronization tools (including ones not designed specifically for SharePoint) as you are now simply ensuring a sync takes place between two accessible drive locations.
There are also some applications that support synchronization from SharePoint to drives including Colligo Briefcase https://www.colligo.com/products/sharepoint/colligo-briefcase-for-windows/