Open Source Document Management Systems?

Lancer asks: "I sat in on a product demonstration this morning for a Document Management solution my employer is considering. The product looked very nice, lots of useful features for creating a paperless office. Then the hammer came down - $40,000 to get started, of that less than $10,000 would be actual hardware - ouch! So, my question is, are there any free solutions available for document storage and retrieval? If you're not familiar with the concept, these systems generally involve scanning a document (then throwing it away, hopefully), running it through OCR, and putting it into some sort of database (these vary wildly in capability from vendor to vendor), and being able to query the documents out later." Actually, a few don't even bother to OCR, and just store raw scans in the database. Surely something can be built from existing open sourced tools that can do this for less than half this price!