From the video description:
Hot Melt Glue Gun HMA (Hot Melt Adhesive) Extruder to make a 3D Printer. It is based on a $3 Walmart Low Temperature Mini Hot Glue Gun. The extruder is driven around by a 3 axis CNC router made from plans from http://solsylva.com/cnc/13x13x5.shtml . The whole thing is driven by an Arduino Uno with a custom set of Shields, a single stepper driver based on a ULN2803 and a parallel port adapter board to drive a 3 axis HobbyCNC stepper driver board. I am using the Teacup firmware that has been customized to driver the ULN2803 stepper driver for the extruder (E axis). All is orchestrated by Pronteface on the PC side with G-Code by Slic3r (converts STL 3D Model to G-Code for Pronterface).
Complete step-by-step guide:
Update: I was told in comments on Reddit that this is nothing new. Basically RepRap started its development with hot glue guns. There is much more information in "A history of RepRap development":
Great work and cool DIY project anyway!