Bidirectional filesystem syncing

Everyone knows and loves rsync, the command that lets you clone a directory tree to another disk or system with the ability to keep the clone fresh in an incremental and bandwidth-efficient manner. Sometimes, however, you want to sync in the reverse direction. With bidirectional filesystem syncing tools, there is no primary filesystem -- you just tell the tool to make sure both target directories, or clones, are identical. Here's a hands-on look at two tools designed to accomplish that task: DirSync Pro and Unison.