WSSV3FAQ

http://www.blackbladeinc.com/en-us/products/docBlock/Pages/default.aspx

Potential users are advised to read the entire description at the site and/or the PDF file linked to there.
(This extract is my attempt to give a brief indication of what the product is for.)

"The docBlock provides virtual document support for the SharePoint platform. The docBlock is a software / hardware appliance that connects to your SharePoint farm over a network connection."

"The docBlock extends the SharePoint platform by providing a virtual document service to your farm, allowing you to create a master document in any document library as well as a hierarchy of document sections that can be updated separately by different individuals. This allows multiple people to edit and maintain the same document at the same time, without having to check in the document."

Pricing (Oct 2008): unknown
(the only price on the site is for another product)