KnowledgeTree is an enterprise-level open source document management application built with PHP & uses MySQL for storing the data.
It enables reaching documents via web, desktop or Microsoft Office applications (via an add-in) & sharing them become easier with integrated dicussion forums, e-mailing, tagging & more.
With a role-based permission system, every user can view the documents they are permitted to, updates on documents are tracked & every user can connect with a different language to the system which is great for virtual, multilingual offices.
KnowledgeTree accepts adding documents in bulk (zipped), has built-in support for scanners & OCR softwares. Also, with the API support, it can be integrated with 3rd party softwares.
Besides those powerful features, the application has a powerful search module which works on numerous document types (Microsoft Office, PDF, OpenOffice, XML, HTML, RTF, text) & offers solutions to improve workflows.