This is a 3D printer attachment to a CNC machine that utilizes a standard caulk gun tube for producing 3D printed objects.
The project page for this item located here:
Adventures in 3D Printing
Here is a picture of the caulk tube extruder attached to my CNC mill.
Here is a picture of an item made with the caulk extruder.
Finally a video of the extruder in action.