For quick syncing of critical files between multiple systems, it's hard to beat a , which is a simple folder that connects to a cloud service for automatic synchronization. Just put any file in your drop-box folder, or create any subfolder in it, and that item will instantly appear in the corresponding drop-box folder on any computer or mobile device using the same account.

Drop-box services differ from folder-syncing services in that they sync subfolders and files only within a single drop-box folder; they don't allow you to designate any other folders on your drive for syncing.

The best drop-box software around is the aptly named , which comes with 2GB of free storage that you can upgrade to as much as 8GB by spamming your friends to try it out. (Good luck, though; most of your friends are probably already using it.) Amazon recently launched , which looks like a serious contender with 5GB of free storage.