Here is a handy plugin that integrates your WordPress site with cloud services such as Google Drive, Amazon S3, and Dropbox. WordPress Cloud Manager lets you access your cloud drives directly from the dashboard. You can allow others to upload files but limit file size and type.
This plugin lets you share your folders with your users. It has multiple good looking themes for you to choose from. With notifications, admins are notified when a user uploads a file. Cloud Manager also lets you edit files and images, view documents, and convert files.