Remository by Martin Brampton is a very stable extension that has been around for a considerable amount of time. Remository's strength is in its ability to upload, hold and download files like documents and images. In the words of the developer:
A component that is easy to install and use, yet has an unparalleled depth of features for a powerful file repository. The latest version adds the ability to play audio/video files as well as to download them. There are related modules and plugins to complement the main component. Remository supports the secure hosting of local or remote files for download by site visitors. Files can be uploaded by users, and locally hosted files can be stored in either the database or the file system. Thumbnails can be uploaded along with files, or automatically generated with uploads of image files. Displays can be customized, and Remository includes a very flexible access control system so that upload, download and editing can be managed in almost unlimited ways.
To visit their site go to www.remository.com