The Camera Accessory Mounting System (or “CAMS” for short) is a series of connecting blocks that work with standard 1/4“ hardware (nuts, bolts, screws) to allow mounting of accessories to cameras.

There's a few blogs posts with details:

• http://rasterweb.net/raster/2014/02/24/a-new-arm/
• http://rasterweb.net/raster/2014/03/05/a-new-arm-part-ii/

Files on Thingiverse:

• http://www.thingiverse.com/thing:271619

• Pete Prodoehl