Recently, a potential client asked us if we could recommend a viable open source document management system (DMS) for their needs. Despite our deep experience with Open Source business solutions, I didn't have one to recommend. I think that is primarily because so few businesses have need for a true DMS - even if they could benefit from it. As I thought about it, we could benefit from one because we save so many files and even have an elaborate naming scheme for versioning.
So, I went on a quest to see what I could find. The systems I chose have the following features: Easy to use, Flexible to store any file, Versioning, Ability to handle large Volumes of Data, Customizable Meta Data, Document Text Search (including PDF), and Provide a Web Interface for Universal Access. Here are the ONLY two candidates I found:
KnowledgeTree: http://www.ktdms.com/products/ktdmsfeatures
Comments: Mature and well-supported open source solution. Supports grouping of data, meta-tags, versioning, and has some nice time saving features for dealing with large volumes of data. I particularly like the ability to have pre-defined data requests per document type - as well as the 'discussion'. It doesn't have anything specific for media management - but the system's flexibility keeps that from being an issue. Per your requirements, it also has some basic collaboration through checkin/out and 'work flow management'.
Support: Commercial Support available, as well as commercial tools for better integration into a Windows/Client environment.
jLibrary: http://jlibrary.sourceforge.net/4/index.html
Comments: Looks to be a very promising solution. jLibrary combines a rich feature set you'd expect in a document management system with an easy to use interface. It also has a nice feature of providing access via a client, as well as the web. jLibrary allows for large volume management, meta-data for groups, and even a relationship manager(separate from meta and categories). Currently, the product is in beta - so it may be good to wait for the first production release.
Support: Commercial support is available