Dropbox transfer notifies you of views and downloads. I'm a paying user and using transfer to send files to friends. It's very useful.

Transfers auto-expire after a week and links invalidate so it's maintenance is minimal for the normal user.

The annoying thing is that you can't turn off those notifications, which pop up in your tray and e-mail box. If there were options for turning off notifications it would be perfect for my use case.

This can be password protected and have an expiration date. I don't think Dropbox normally has download notifications, and this is possibly more friendly to receivers without a Dropbox account and can be company branded.

For all the bells and whistles, you need to be a "Pro" user. I'm using "Plus", and it's fixed to one week, without any password and branding.