Cloud Storage Services incompatibility

We found a problem created because the many options already availables to share your files using a cloud service like Dropbox , Skydrive or Box or Google Drive.

The problem is that my friens and coowrorkers are using diferent service and we “have”. create a second or third account if we want to share a folder or files.

We can use the informal and no safe option to share trough a link but it is not what we need. We are looking for some kind og wep site that could works like an neutral interface that allow my friend to share me a dropbox file with out force me to create a Dropbox account. what do you think ?