Of course the first of these applications  is Dropbox. Dropbox has been around for a while and is used by millions. Once you download and install the application there will be a folder on your computer labeled Dropbox and everything you save in that folder will be uploaded to a server. You can add as many computers to that account as you would like. Dropbox gives you 2GB free with an option to purchase more space. Dropbox is a little expensive. Maybe this now competition will force them to lower the price. Dropbox has client software for Windows, Macs, Linux, iOS, Android and Windows Phone I think.

See the post about Skydrive…