Dropbox is an online storage service, that gives you 2GB of free space where you can sync files, share and make backups. You can then also access your files remotely from a browser or mobile device.
Dropbox is one of the best developed online storage solutions, and is very user friendly as well as having tons of great features. Any document you edit in your Dropbox folders is updated across all the devices you use the application. Dropbox also keeps 30 days of file history, so if you don't like a change, you can find old versions easily.
Dropbox is also great for sharing - you can give someone a direct link to any file, or invite people to share a file you have. It's useful for collaboration as well as things like sending your friends and family photos.
Another useful feature of Dropbox is safety: All your Dropbox files are stored safely online, so are protected in case something goes wrong with your computer. 2GB of space isn't enough to backup a computer, but it is enough to keep some important files. As well as the web app, there is a desktop widget alongside iPhone, Android and Blackberry apps.
Dropbox is a really smart online storage system, and an excellent addition way of sharing and accessing files wherever you are.