Unlike to Dropbox and SkyDrive where a folder is shared only between group members and only they can upload files, you can use OneTimeBox for sharing folders publicly where anyone can upload files. Yes OneTimeBox, is an awesome webservice that allows you to creates disposable open web folder where anyone can easily add files, only the condition is they must follow its unique URL i.e. the URL of your shared folder. Even there’s no registration required. All you will be needing to do is share the unique URL of your webfolder with your friends and they can access and upload files, also they get the delete permissions.