Windows: QuickSync is a minimal synchronisation tool that lives in your system tray, allowing you to quickly bring it up and start syncing your data. To get started, all you have to do is drag and drop a folder onto its main window.
Once you've done that, you've set your source. From there you'll be able to set your destination location and start syncing. QuickSync is particularly handy when it comes to sync conflicts, as it uses smart name detection to recognise missing and moved files during sync and has several options for resolving conflicts. Once you get your sync plan set up, QuickSync can schedule it so it's entirely automated and you don't have to mess around with it again. But if you want to, you can easily by just finding your settings resting quietly in your system tray.
QuickSync is a free utility that's available right now for Windows 7, Windows Vista and Windows XP.