Windows/Mac only: Freeware application and web service Dropbox instantaneously backs up and syncs your files over the internet and to any computer. After you install the application, it will create a Dropbox folder on your hard drive. Any file you put inside that folder will automatically be synced and monitored for changes, and each time a change is saved, it backs up and syncs the file again. Even better, Dropbox does revision history, so if you accidentally saved a file and wanted to revert to an old version or deleted a file, Dropbox can recover any previous version. See the video above for a full demonstration.