Dropbox is an on-line file storage and sharing service. 2GB of Dropbox is available for free, with subscriptions up to 100GB available. Shared folders allow people to work together on the same projects and documents.
Dropbox files are also available off-line, and folders can be synced between multiple computers and mobile devices. Dropbox therefore can be used as a backup mechanism for important files, although it is by no means a complete solution.