Dropbox is a cloud storage system where you can backup your files and folders on their servers and access them in real-time on Windows and Linux machines.
It integrates with the operating systems desktop manager and allows you to add/remove files just like a folder on your computer.
It’s free to try out and you’ll have 2GB of storage completely free; if you invite your friends using the referral scheme you get an extra 250MB per person (up to 3GB) so in theory you could have 5GB of online storage for nothing.
The good thing about Dropbox is that it supports Windows, Linux, Mac and even your iPhone and allows you to share files between these devices. It’s pretty good considering it costs you nothing.