Free to Sync

Unison—Unison synchronizes files across UNIX and Windows platforms (www.cis.upenn.edu/~bcpierce/unison).

rsync—This open-source UNIX utility provides fast file transfers; it requires a wrapper and configuration for Windows use (samba.anu.edu.au/rsync).

Windows Vista Sync Center—Vista's Sync Center lets you synchronize files between PCs, laptops, and mobile devices (windowshelp.microsoft.com/Windows/en-US/Help/1074e034-1bcf-4dfb-93c3-46ec7df97d371033.mspx).

Windows XP Professional Offline Files—XP's offline-files feature helps you synchronize files over a network (www.microsoft.com/windowsxp/using/mobility/learnmore/offlinefiles.mspx).

Microsoft SyncToy 1.4—SyncToy helps you copy, move, rename, and delete files between folders and computers (www.microsoft.com/downloads/details.aspx?familyid=E0FC1154-C975-4814-9649-CCE41AF06EB7&displaylang=en).

Robocopy—This command-line tool is intended for copying folders (with an optional argument filter for use with filenames). It's available as a standard feature in Vista and as part of the Microsoft Windows Server 2003 Resource Kit (www.microsoft.com/downloads/details.aspx?familyid=9d467a69-57ff-4ae7-96ee-b18c4790cffd&displaylang=en).