Dropbox

Link: https://www.dropbox.com/

Have you ever been working on a project between friends where you tried to e-mail up-to-date files between members? Or have you had your files on a USB stick and lose it? Dropbox can help in these and many more situations. Think of it as an online external hard-drive. Once you install it, it acts as any normal file on your computer. Any time you make a change, it updates the same file on their servers. What's even cooler is that it will update all the devices that have access to that same file. You can share files between friends and be sure that all of them have the latest versions of the files. Also, if you USB stick or computer die, there will be a backup online. And if you don't want to install the program, you can upload/download files using the web interface.

This is a must have for high school and college team projects! And it's a great way to backup your files.