Use CloudOsys to let your Visitors upload files directly to your Web site where they can share, add comments, manage and download. No requirements, you just need web hosting. There is Live Demo available. Free version is available in .zip format containing all the scripts. Just unzip, upload and run the installer. Also, subscription offer is for gaining access to download the Advanced version. The Advanced version comes with PHP scripts, admin tools for enabling/disabling users' accounts, and tools to look through all public and private files. But still, there's a Lite version which is free.
