With the release of CompleteFTP 8.0 recently, collaborative file-sharing has been added to CompleteFTP's many capabilities (in the Professional and Enterprise editions).
CompleteFTP now ships with a file-sharing client called CompleteBox. A user account must be set up on the CompleteFTP server, and the CompleteBox client installed on the user's local machine. The user enters their credentials, and they can now share their local files by either right-clicking on a file and selecting the "Share with CompleteBox" menu item, or by explicitly selecting a file from the CompleteBox client.
The selected file is uploaded to the CompleteFTP server and a unique URL for the file is generated. The user can then email or send the URL to anyone for downloading.
By default, one user license ships with CompleteFTP, and further user licenses can be purchased. More details can be found here.