Nexus

Nexus is an open source, web-based, extensible document management system that you can install on your own host. Easy-to-use, simple to administrate and incredibly powerful, Nexus can centralize and bring order to your document library. Unlike X-Drive, Box.net and all the other hosted solutions Nexus gives you the power to deploy wherever you want leveraging existing hardware and technology. The power of Nexus lies in its permissions system which applies file/folder permissions based on Nexus domains (which are made up of an Organization/Group pair). Each user is a member of a domain and therefore subject to its restrictions. Nexus is built on cross-platform, open-source technology - it will run on any machine: Windows, Unix-variants, Macintosh, etc. as long as that machine has PHP 5 or later, MySQL 4 or later and any type of web server that supports server-side scripting (IIS or Apache, for example)