Undoubtedly one of the best apps to come out of Redmond, Windows Live's freeware FolderShare is a fantastic tool for keeping folders synchronized across multiple computers and multiple platforms. Although we're just getting around to the product review now, for people who don't know what the program can do I figured this would be a good time to highlight some of the more useful and interesting features.
Also important: FolderShare is still in beta, but sported none of the bugginess that plagues most betas.
While both the PC and the Mac versions do the same thing, which is allow you to send a file from one computer to another simply by dropping it into a folder, the Mac client surprisingly offers more on-the-fly options. To get started, download the OS-appropriate client. FolderShare then asks you to create an account when you install, and it was one of the least invasive account-creation dances I've done. There's no email with a secret link that you need to confirm, simply register and go.
All configuration tweaks were dead simple to manage, too. The online interface means that you can create new folders to share as you need, and changing a folder from manual sync to automatic syncing was a one-click affair. As mentioned above, the Mac client lets users change the computer name, toggle encryption, and manage the transfer logs. Windows users can change the computer name online, but their desktop client limits them to configuring proxy settings and ports. Fancy, but those tools are also available on the Mac.
Although I liked that FolderShare respects your default browser settings, users should realize that it's not very good for collaborative work unless both users are online simultaneously. If one of the shared computers is off or hibernating, files won't be synchronized. For users who leave their computers on all the time, though, it's a fantastic tool that re-affirms that Microsoft can, in fact, get things right.