Synchredible is freeware application by which you can synchronize or backup your files with your system/network with USB or any application. Once this application is installed only you need to connect the usb device or connect to network it will automatically sync without any user interaction. It detects duplicate entries automatically so both the device has same data and your device is synced.

Some features:

Data synchronization
synchronizes your data/folders the easy way, scheduled jobs for data synchronization and data backup. Network support is integrated for data synchronization between local area networks (LAN).
Real synchronizations
Support both one and two directions synchronizations. Will recognize changes automatically update
Synchronization as backup strategy
Data synchronization of files and/or folders, but also for data backup operations onto internal or external drives (USB1.1/2.0 supported).

You can know more or download: Synchredible Homepage.