FreeFileSync
FreeFileSync is a free Open Source software to synchronize files and synchronize folders available for Windows, Linux and Mac OS X.
rsync is a software application for Unix which synchronizes files and directories from one location to another while minimizing data transfer using delta encoding when appropriate.
Productivity Developer Tools Utilities Backup and Sync
FreeFileSync is a free Open Source software to synchronize files and synchronize folders available for Windows, Linux and Mac OS X.
Free Open Source Mac OS X Windows Linux Debian CentOS Ubuntu openSUSE
Allway Sync is a file and folder synchronization software for Windows.
Freemium Windows
back in time is a simple backup tool for linux inspired from flyback and "timevault". the backup is done by taking snapshots of a specified set of directories.
Free Open Source Linux
Areca Backup is a file backup software that supports incremental, image and delta backup on local drives or FTP servers.
Free Open Source Windows Linux
Create Synchronicity is a nice, lightweight backup program with a very user-friendly - yet powerful - interface, that synchronizes files and folders extremely quickly (it can even recognize paths such as "MyUSB"\MyFolder, and...
Free Open Source Windows
ChronoSync can synchronize, backup, and create bootable backups to almost anything you can connect to your Mac: select cloud services, other Macs, NAS drives, external drives, PC's or anything you can mount as a volume.
Commercial Mac OS X
Performs full system imaging, incremental backups, local and network backup locations, and bare metal recovery.
Free Windows