Open source Sync tools for Windows

Synchronicity

Create Synchronicity is an opensource application developed in VB.NET to synchronize files and folders across different locations. (GPL)

Windows

Unison

Unison is a file synchronization program. It is used for synchronizing files between two directories, either on one computer, or between a computer and another storage device. (GPL)

Linux - FreeBSD - Windows - MAC OS X

2 applications