#4 Dropbox

Dropbox offers cloud storage, file synchronization, and client software. It allows users to create a special folder on each of their computers, which Dropbox then synchronizes so that it appears to be the same folder, with the same contents, regardless of which computer is used to view it. Files placed in this folder also are accessible through a website and various mobile applications. Dropbox provides client software for Microsoft Windows, Mac OS X, Linux, Android, iOS, BlackBerry OS and web browsers, as well as unofficial ports to Symbian, Windows Phone and MeeGo.

Dropbox only comes with 2GB of free storage, but you can get more storage by bringing new users to Dropbox. If you want more room, Dropbox charges $9.99 a month, or $99 annually for 100GB, and similarly priced deals for up to 500GB.

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