File Upload and view with access control

I'm looking for a browser based tool where a user (admin) can upload files to the server. The admin should be able to select which registered users have access to which files.

Then when other users log in they should be able to view only the files designated to them.

Is there any existing product that does this and is available for integration.

I could do this in PHP, but I was wondering if I'd be re-inventing the wheel and hence looking out for existing solutions that would probably have better features.